Scheduling infrastructure, not just a booking page - Cal.com is the leading open-source scheduling platform. Share a link, attendees pick a slot, and real-time sync against Google Calendar, Outlook, and CalDAV prevents double-booking. Beyond the basics it covers team workflows: round-robin distribution, collective availability across multiple hosts, recurring meetings, and routing forms that ask bookers questions and send them to the right team member - the feature sales and support teams usually pay enterprise prices for. Paid bookings run through Stripe, video calls through the built-in Cal Video (Daily.co) or Zoom and Google Meet, and an app store connects 100+ tools including HubSpot, Zapier, and n8n. The API-first architecture with webhooks and embeds makes it practical to build scheduling into your own product, white-labeled with your domain and branding. Built on Next.js and Prisma over PostgreSQL, translated into 65+ languages, with the self-hostable community codebase maintained under an open-source license.

With over 47,000 GitHub stars, Cal.diy is the fully open-source community fork of Cal.com that strips away every proprietary license gate and enterprise paywall to deliver a pure MIT-licensed scheduling platform you completely own. The booking engine supports individual event types including recurring events, seated events with capacity limits, and paid bookings through Stripe and PayPal, all backed by customizable availability schedules with date overrides, buffer times, minimum notice periods, and travel schedule support. Calendar synchronization is bidirectional across nine providers — Google Calendar, Outlook and Office 365, Apple Calendar, CalDAV, Lark, Feishu, Zoho, Exchange, and ICS feeds — so every booking automatically appears on your existing calendar while blocking conflicting slots. Video conferencing links generate automatically for Zoom, Google Meet, Microsoft Teams, Webex, Jitsi, Daily.co, Whereby, and Huddle01, eliminating manual link management. The automation layer connects through webhooks, Zapier, n8n, Make, and Pipedream to CRM platforms like HubSpot, Salesforce, and Close, messaging services including Discord, Telegram, and WhatsApp, and analytics tools such as Google Analytics 4, PostHog, and Fathom. The entire application is built on the T3 stack — Next.js for server-rendered pages, tRPC for end-to-end type-safe APIs, Prisma for PostgreSQL database access, and Tailwind CSS for the responsive interface. Unlike Cal.com's open-core model, Cal.diy requires no license key and includes no gated features. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Service businesses get a booking page without per-booking commissions or monthly SaaS fees from Easy!Appointments, the self-hosted appointment scheduler. Customers pick a service, provider, and open time slot from a clean web form; the system enforces working plans, breaks, and booking rules you define per provider, then confirms by email to both sides. The structure fits real service organizations: multiple providers with individual schedules, multiple service types with their own durations and prices, and admin/secretary roles for front-desk management. Two-way Google Calendar synchronization keeps each provider's external calendar authoritative - book in Easy!Appointments and it appears in Google Calendar, block time in Google and the slot disappears from the booking form. Version 1.6 adds SMS notifications and payment support, and a REST API opens the scheduling data to custom integrations. Built on PHP (CodeIgniter) with MySQL, it installs in a single folder and can share a database with your existing site; a WordPress plugin embeds the booking form directly in pages or posts. The interface ships in dozens of languages with time-zone handling throughout. GPL-3.0 licensed and free for commercial use - a helpdesk, clinic, salon, or consultancy runs its whole booking workflow on its own server.

Built on Elixir's fault-tolerant OTP runtime, Tymeslot delivers the complete scheduling toolkit that Calendly charges for and Cal.com relicensed away from open source in 2026. Share one booking link and let clients pick available slots — your calendar stays synchronized and double-bookings disappear automatically through real-time availability checking against Google Calendar, Microsoft Outlook, and any CalDAV server including Nextcloud. Meeting types support configurable durations, buffer times, and availability windows that clients can book without email back-and-forth. Phoenix LiveView powers the real-time UI with WebSocket connections that update instantly as bookings arrive, without client-side JavaScript framework overhead. The platform attaches Zoom video rooms to confirmed bookings through your own Marketplace app credentials, sends confirmation and reminder emails via SMTP, Postmark, SendGrid, Mailgun, or AhaSend, and supports custom booking page themes with embed options for integration into existing websites. Circuit breakers, connection pooling, and graceful degradation maintain availability during provider outages. Authentication supports local accounts, GitHub OAuth, and reCAPTCHA protection on public booking forms. Self-hosting deploys as a single container with PostgreSQL embedded — no separate database container required. Two named volumes persist uploads and database state, while the same image powers the managed cloud at tymeslot.app so self-hosted users get identical features without a crippled community edition. Deploy via Docker, Cloudron with automatic updates, or Railway from a community template. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

What Doodle did before ads and paywalls took over: Rallly (three L's) lets you propose a few dates, share a link, and watch an availability grid fill in - no email threads, no forced accounts, no "$6.95/month to remove ads." The availability grid makes the winning slot obvious at a glance, comments on each poll keep the "I can do Tuesday if we start late" discussion attached to the decision instead of buried in chat, and email notifications fire as votes and comments arrive. When consensus lands, finalize the winning option and everyone gets notified. The stack is modern TypeScript - Next.js, tRPC, Prisma over PostgreSQL, Tailwind - with a clean, genuinely mobile-friendly UI, dark mode, and community translations in 10+ languages. Self-hosting means unlimited polls and unlimited participants with meeting data on your server rather than a scheduling SaaS. It pairs naturally with Cal.com: Rallly answers "which time works for everyone?", Cal.com handles "book a slot on my calendar." AGPL-licensed.

Mitra is a self-hosted calendar that puts your tasks on the same timeline as your events, so planning a week finally happens in one place instead of two. Drag across empty grid space to make an entry, drag it to move it, and stretch its edges to resize it. Tasks without a date sit in the Planning tab with a due date and an estimate until you drag them into the week. Subtasks and dependencies draw as lines between entries. Availability shading lays your working hours under the grid so double-booking becomes obvious before it happens. Keep calendars inside Mitra with no account behind them, or connect the ones you already use: CalDAV, Google Calendar, Apple Calendar, Notion, Todoist, and Tempo all sync both ways, and published feeds arrive as read-only subscriptions. Lists sort, filter, and change many entries at once. Files attach to entries, guests reply, reminders land as push notifications, and a command palette drives everything from the keyboard. Claude, Cursor, and other AI tools can read and plan your calendars over MCP. Eight languages, right-to-left layouts, light and dark themes, phone install, and OIDC sign-in for several people round it out. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Work, personal, business, and school calendars at different providers double-book because no one system sees your real availability - Keeper solves that multi-calendar collision problem. Its pull-compare-push sync engine aggregates events from Google Calendar, Outlook/Office 365, iCloud, FastMail, any CalDAV server, or read-only iCal/ICS feeds, and pushes blocking events to one or many destination calendars so time slots align everywhere. The design is deliberately content-agnostic - it syncs timeslots, not titles or descriptions, so a personal appointment shows as busy time on your work calendar without leaking details. Sync logic is clean: events Keeper creates carry a traceable UID suffix, deletions propagate, and orphaned entries are purged automatically. A token-authenticated aggregated iCal feed combines selected calendars into one subscribable URL for Apple Calendar or Thunderbird. An optional MCP server gives AI agents read-only calendar access over OAuth 2.1 - list calendars and query events by date range, with no write capability. Built with Next.js and Bun under AGPL-3.0, the standalone Docker image bundles web, API, cron, worker, Redis, and PostgreSQL in one container, and self-hosting unlocks every Pro feature - unlimited calendars and one-minute sync intervals - for free.

Calendars, to-do lists, journal entries, and contacts, synced over the open CalDAV and CardDAV standards nearly every client already speaks: Radicale is a small pure-Python server that works with Thunderbird, DAVx5 on Android, Apple Calendar and Contacts, GNOME, and many more. Its defining design choice is radical simplicity: there is no database. Events live as plain .ics files and contacts as .vcf files in an ordinary folder structure, which makes backup a copy command, migration a move, and disaster recovery a matter of reading text files. The server works out of the box with no complicated setup, then grows as needed: flexible authentication (htpasswd files among other methods), per-collection authorization rules, TLS-secured connections, and a plugin system for extending storage, auth, and rights handling. Built-in limits on parallel connections, file sizes, and failed authentication attempts harden it for network exposure behind a reverse proxy. A bundled web interface handles creating and managing calendars and address books - useful since many clients cannot create collections themselves. Maintained since 2011 with 140+ contributors, GPLv3-licensed, and light enough to run on the smallest VPS or a Raspberry Pi.

Your calendars and contacts do not need a cloud account, and Baikal is the small PHP server that keeps them on hardware you control while still syncing to every phone and laptop you own. The web admin panel is where you add users, create their calendars and address books, and reset passwords, no database editing or config files required. Each person signs in with their own username and password, so an iPhone, an Android phone running DAVx5, and a Thunderbird desktop can all stay in sync without sharing one master credential. Standard well-known redirects mean most clients configure themselves when you type the server address, and the combined dav.php endpoint serves calendars and contacts from a single URL. Events carry the full CalDAV feature set your clients expect (recurring appointments, reminders, attendees, and free-busy lookups), while CardDAV address books keep names, phone numbers, and photos in one place. Because storage is a plain database file or table set, backups are a copy you can make in seconds, and moving to a bigger host is a file transfer rather than a migration project. The same server happily runs for one person tracking a family calendar or for a small office sharing team schedules and a company address book. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

SOGo adds shared calendars, address books, and a modern webmail interface to your existing Dovecot, Postfix, or Cyrus mail setup, turning familiar infrastructure into a full Exchange competitor. Rather than replacing your IMAP and SMTP servers, SOGo layers collaboration on top of them, becoming the missing link between raw mail delivery and what users actually expect from a workplace communication platform. The ActiveSync implementation synchronizes email, contacts, calendars, and tasks natively with iPhones, Android devices, and Windows without requiring users to manually configure CalDAV endpoints. CalDAV and CardDAV compliance ensures Apple Calendar, Thunderbird (via the official SOGo Connector extension), GNOME Evolution, and Android via DAVx5 all connect without plugins or workarounds. The web interface uses AngularJS Material design with responsive layouts, offering folder management, drag-and-drop calendar scheduling, contact groups, resource booking, and delegation. Shared calendars support free-busy lookups, iMIP event invitations, and per-user ACL permissions for fine-grained access across organizational units. Built on Objective-C with the GNUstep foundation, SOGo delivers exceptional performance: hundreds of concurrent ActiveSync connections from mobile devices alongside webmail and calendar traffic with sub-second response times. With 2,095+ stars and 116 releases, the project has proven its stability in production environments supporting thousands of users. The Docker deployment runs alongside PostgreSQL and memcached.

Five mailboxes, five tabs, five passwords: Gofer folds Gmail, Outlook, iCloud, and plain IMAP accounts into one browser tab where every inbox reads as a single, searchable whole. Threads, labels, and drag and drop keep triage fast, and search still finds the receipt from three years ago. Signatures and custom senders shape outgoing mail, scheduled sends wait for Monday morning, and a thread in another language translates in place. The calendar keeps pace with your mail: Google, Outlook, and CalDAV events sync both ways, invitations land in the inbox, and an RSVP or a Meet or Teams link attaches without leaving the message. Contacts follow the same rule through Google, Outlook, and CardDAV sync, so the address book you fix once is right everywhere. One install can serve a household or a small office, with separate users, encrypted credentials, blocked remote images, and passkey or authenticator sign-in for anyone who wants it. Classic, Minimal, and retro Express themes, flexible layouts, and push notifications make the daily inbox feel personal rather than administered. Leaving stays easy too: mailboxes export as mbox, mail moves between accounts, and a whole setup imports into another Gofer. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

GroupOffice checks your whole company in at one address: mail, meetings, projects, invoices, and files behind a single login on your own server. The built-in mail client saves messages straight onto projects or contacts, signs and encrypts with S/MIME, and shares folders and accounts across the team. Shared calendars offer team views, bookable resources, and video meetings, while address books carry custom fields and comments so customer knowledge survives staff changes. Projects gather their tasks, files, and discussions in one place, track hours as work happens, and turn those hours and costs into invoices and reports. Support tickets arrive from your website or by email and stay organized by team, and newsletters compose campaigns from templates filled with your own data. Files co-edit in the browser through OnlyOffice or Collabora, connect to desktops over WebDAV, and sync to native phone and computer apps over open protocols. Two-factor authentication, encryption, and a module system you can extend with your own tools keep the office private and shaped to how you actually work. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Conference rooms, equipment, boats, and even people can be reserved through LibreBooking, a self-hosted scheduler that keeps double bookings off the calendar. Schedules define bookable time slots with custom layouts and seasonal availability, while each resource carries its own minimum and maximum duration, buffer time, lead time, capacity, and optional approval step. Check-in and check-out can release unclaimed slots automatically, and blackout times close resources for maintenance. Quotas stack limits by hours or reservation count, credits meter peak and off-peak usage, and users can buy credits through Stripe or PayPal. Accessories such as projectors or chairs ride along with a booking under their own quantity limits. Groups carry application, group, resource, and schedule administrator roles, and custom attributes extend reservations, resources, and users with text, dropdown, date, or checkbox fields. Reports can be charted, exported to CSV, printed, or emailed, and public resources publish RSS and iCalendar feeds for Outlook and Thunderbird plus an embeddable calendar snippet. A tablet view beside a door shows live availability for on-the-spot booking, a monitor view fills lobby screens, and a Slack command starts a reservation. Sign-in options include LDAP, Active Directory, OAuth2, and SAML, and the REST JSON API automates bookings. Users can join waitlists, request reminder emails, and accept terms of service before booking, while six color themes restyle the interface. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Seatsurfing brings desk booking, room reservations, and parking management to interactive floor plans across multiple office locations, solving the coordination headache of hybrid work. The Go backend serves two React/TypeScript frontends through a single Docker container on port 8080: a Booking UI built as an installable Progressive Web App for mobile and desktop reservations, and an Admin UI for floor plan configuration, capacity enforcement, and analytics. Interactive floor plans accept uploaded office layouts where administrators visually place bookable spaces with per-space metadata and availability rules. Multi-location support handles organizations with distributed offices across multiple buildings and cities. The buddy system displays which colleagues have bookings on a given day, enabling team coordination without manual communication. Capacity management enforces occupancy limits per area with automatic denial when thresholds are reached. SSO integration supports OIDC and OAuth2 providers including Microsoft Azure AD, Keycloak, and Authentik for enterprise identity federation. Microsoft Teams and Confluence integrations embed booking directly into collaboration tools employees already use daily. The REST API enables automation and custom integrations, while the analytics dashboard tracks utilization rates, peak hours, and booking patterns. Docker Compose deployment requires only a PostgreSQL database with multi-architecture images supporting amd64 and arm64. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

From the call for abstracts to the badge handed over at the registration desk, Indico handles every step of running a conference, plus the weekly meetings and one-off lectures that fill the calendar around it. Events live in a nested tree of categories, and access rules can be set per category, event, session, or single contribution, with custom roles inside each event. Speakers submit abstracts, track reviewers score them against questions the organizers define, judges accept or reject them, and accepted talks become contributions that sit in a drag-and-drop timetable of color-coded sessions. Registration forms are assembled field by field, carry fees, and take payment through PayPal, Stripe, or SIX Payment plugins; attendees get QR-coded tickets, and a badge editor prints name tags for the whole room. A paper reviewing workflow collects full papers. Meeting pages keep minutes and slide decks attached to the talk they belong to. The room booking module adds approvals, recurring reservations, and audiovisual equipment, and the Zoom plugin creates online sessions straight from an event page. Calendar views span a month, week, or day, filter by category, and export to iCal for subscriptions. Scripts pull event data from the HTTP export API as JSON or XML with personal API tokens. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Unlike a calendar alert that rings on one phone, a MIND reminder reaches any of 100+ services, including email, Pushbullet, BlueSky, Cisco Webex Teams, and SMS gateways, from a self-hosted reminder app that you control. Normal reminders fire with second precision once or repeat every few days, once a year, on chosen weekdays, or on a custom cron schedule, while static reminders wait for a button press, so a single tap can tell the family that you are running late. Templates store colour, title, services, and text for fast creation, and the colour-coded library can be searched and sorted, with each reminder enabled, disabled, or tested on demand. Time zone changes, including daylight saving shifts, are accounted for, and sends that fail on a connection error are retried every two minutes until they succeed. Several users can share one instance: the admin panel handles accounts and registration, login lifetime, reverse-proxy URL prefix, debug logs, and scheduled database backups that can be exported and imported, and sign-in supports two-factor authentication. A documented REST API covers reminders, templates, notification services, and static triggers, and the web interface adapts to phone screens. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Replace a dozen household subscriptions with one app that keeps your family's tasks, calendars, meals, budget, and shopping in a single private place you control. Nineteen modules cover the daily rhythms of a household: assign chores with deadlines and priorities, plan the week's dinners and push the ingredients to a shared shopping list in one tap, track income and expenses by category with automatic subscription renewal warnings, and log health activities from vitals to medications. Two-way sync connects to Google Calendar via OAuth, iCloud and Nextcloud via CalDAV, and Outlook via Microsoft Graph, so every family member's phone shows the same schedule without switching apps. CardDAV keeps contacts in sync with external address books. The budget module handles accounts, loans, split expenses, and per-category planning with savings goals and month-over-month comparisons. Documents attach to tasks, receipts link to transactions, and a checked-off grocery item books itself back into the pantry inventory with its quantity. A Kanban board, recurring task schedules, and a rewards ledger that pays out points for completed chores keep kids and adults accountable. Wall mode turns a kitchen tablet into a glanceable family dashboard, and the Immich screensaver shows your own photos when the screen goes idle. API tokens and a built-in MCP endpoint let AI agents and third-party tools interact with every module programmatically. Deploy on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Your family's shopping list, calendar, chores, meal plan, and budget share one home in OpenFamily, a self-hosted organizer that replaces subscription family apps with software you control. At the store, everyone ticks items off the same shopping list, with automatic categories, prices, reusable templates, and a store mode that groups items by category, and every phone updates instantly. At home, recurring tasks with three priority levels go to a specific family member, and in Pocket money, approved chores earn points that convert to payouts and savings goals. The calendar offers a monthly view per member, handles recurring and all-day appointments with up to five reminders each, follows Google, Outlook, or iCloud calendars by address, imports .ics files, and publishes its own iCal feed. Recipes can be found by typing the ingredients you already have, then dropped into a weekly meal plan. At month's end, the budget shows recurring income and expenses, per-category limits, charts, and a Kakeibo view. A kiosk display turns a wall tablet into a read-only board of today's schedule, meals, tasks, and who's where, alongside sticky notes from the family. Member profiles store allergies, vaccines, and emergency contacts, and parent and child roles keep the budget read-only for kids. Mealie, Tandoor, Home Assistant, Grocy, Nextcloud, and Immich connect in one click, and an optional AI assistant handles plain-sentence requests. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.