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.

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.

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.

One binary replaces your booking link and your meeting room: Calnode is a complete scheduler you run yourself, small enough to audit and cheap enough to forget. Create event types with durations, custom questions, and locations, set DST-correct availability with date overrides, and share a booking page where guests pick a slot, reschedule, or cancel without an account. Two-way sync with Google Calendar, Microsoft 365, and CalDAV checks real free and busy time across every connected calendar, then mints Meet or Teams links automatically. Teams route bookings round-robin, collectively, or by priority, while paid event types collect through Stripe before the slot confirms. Choose Calnode Rooms and the meeting itself happens in the browser on your LiveKit server, with host controls, consent-aware recording into your own storage, and an AI notetaker that files a transcript and summary on the booking. Agents get first-class access through the REST API, HMAC-signed webhooks, and a native MCP server, and visitors can even book by describing a time in plain language. Everything runs from one static binary and one SQLite file with streaming Litestream backups. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

Share a link, and let people book time with you without the email volley that usually decides when a meeting happens. calrs connects to the calendar you already use, whether that is Nextcloud, Fastmail, BlueMind, iCloud, or any other CalDAV server, computes your real free and busy times from synced events and your availability rules, and shows guests only the slots that genuinely work. Create event types for intro calls, support sessions, or coaching, each with its own duration, buffers, minimum notice, booking limits, and confirmation mode, then publish them on your public profile or keep them private behind single-use invite links. Teams get round-robin scheduling that picks the least busy member, collective meetings that require everyone free, and dynamic group links that intersect several calendars on the fly for a one-off call. Guests pick a slot in their own timezone, receive HTML email with calendar invites attached, and can cancel or reschedule themselves from the confirmation email, while you approve pending bookings from the dashboard or straight from your inbox. When a slot looks wrong, the availability troubleshooter draws a timeline showing exactly which event or rule blocked it. Reminders go out before meetings, credentials are encrypted at rest, and the whole interface speaks ten languages with seven themes. 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.

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.

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.

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.

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.

Kurrier unifies email, calendars, contacts, and file storage in a single web interface that connects to any email provider you already use. The Next.js frontend with Nitro API worker deploys via Docker Compose on PostgreSQL and Redis, delivering a cohesive workspace where IMAP/SMTP mailboxes from Gmail, Outlook, or corporate servers sit alongside transactional providers like AWS SES, SendGrid, Mailgun, and Postmark. Automatic inbox building handles threads, attachments, sent items, and deletion sync through persistent background polling. The CalDAV backend enables full two-way calendar synchronization with iOS, macOS, Android via DAVx5, and Thunderbird, supporting event invitations, RSVP processing through the inbox, timezone-aware scheduling, and contact-aware attendee linking. CardDAV contacts sync bidirectionally across all devices with unified name, avatar, and email resolution. Kurrier Drive provides integrated file storage through WebDAV locally or S3-compatible backends for cloud storage. Multiple identities and domains let you manage several email accounts from different providers in one interface, with fast local search indexing subjects, senders, and content without dependency on external APIs. The API-first architecture exposes clean endpoints for automation and custom integrations. 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.

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.

Backed by nearly 30,000 GitHub stars and powering millions of meetings through meet.jit.si, Jitsi Meet is the open-source video conferencing platform that runs entirely in the browser with no plugins or downloads required. The WebRTC-based architecture delivers HD audio and video through the Jitsi Videobridge selective forwarding unit, while Prosody handles XMPP signaling and Jicofo manages conference focus and orechestration. End-to-end encryption uses AES-GCM 128-bit keys exchanged via the Olm protocol, protecting audio, video, and screen sharing through the Insertable Streams API in Chromium-based browsers. Moderators can split participants into breakout rooms with individual password protection, enable lobby waiting rooms for admission control, set meeting passwords, and track speaker statistics with per-participant talk time metrics. Virtual backgrounds leverage TensorFlow.js body segmentation with WebGPU and WebGL acceleration, automatically adapting quality through device tier detection. Server-side recording and YouTube live streaming run through Jibri, while Jigasi provides a SIP gateway for PSTN dial-in and speech-to-text transcription. The platform includes in-meeting chat with private conversations, polls, raise-hand functionality, emoji reactions, and tile and speaker view layouts. Mobile applications for iOS and Android complement the web client, and both web and native SDKs enable embedding video conferences into custom applications. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 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.

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.