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.

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.

With 14,000 GitHub stars and 81 releases since March 2023, Stalwart is the most protocol-complete open-source mail server available — delivering JMAP, IMAP4rev2, IMAP4rev1, POP3, SMTP, CalDAV, CardDAV, and WebDAV from a single Rust binary that compiles to a memory-safe, zero-garbage-collection executable with predictable latency under load. The SMTP server implements DMARC, DKIMv2, DKIMv1, SPF, and ARC for complete message authentication with automatic DKIM key rotation, while transport security enforces DANE, MTA-STS, and SMTP TLS reporting to prevent downgrade attacks. Built-in spam filtering with statistical classifiers, DNS blocklists, and collaborative reputation databases eliminates the need for external Rspamd or SpamAssassin deployments. Encryption at rest protects stored messages with S/MIME or OpenPGP, and automatic TLS certificate provisioning via ACME supports TLS-ALPN-01, DNS-01, and HTTP-01 challenges without manual certificate management. The ManageSieve server enables server-side email filtering rules, while full-text search indexes message bodies and attachments for instant retrieval. Pluggable storage backends support RocksDB for embedded deployments, PostgreSQL, MySQL, and S3-compatible object storage for distributed architectures. LDAP and SQL-based authentication integrate with existing directory services, and the web administration panel manages domains, accounts, quotas, and DKIM keys. Security audited with memory safety guaranteed by Rust's ownership model. 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.

Stalwart replaces the traditional Postfix + Dovecot + SpamAssassin + calendar-server stack with one Rust binary that speaks every standard mail and collaboration protocol natively. JMAP, IMAP4rev2, POP3, SMTP, CalDAV, CardDAV, and WebDAV all run inside the same process — no glue scripts, no sidecar daemons, no version conflicts between components. The pluggable storage architecture lets operators choose RocksDB for single-node deployments, FoundationDB for distributed clusters, PostgreSQL, MySQL/MariaDB, or SQLite for the data store, S3/MinIO/Azure Blob for message blobs, and Elasticsearch or Meilisearch for full-text search, with Redis or the internal engine backing rate limiters and session state. Security features include S/MIME and OpenPGP encryption at rest, automated DKIM key generation with DNS publication, DANE and MTA-STS transport security, automatic ACME TLS provisioning, granular ACLs, rate limiting, and IP banning. The browser-based admin console manages accounts, domains, groups, mailing lists, SMTP queues, DMARC/TLS-RPT/ARF reports, and every configuration object without touching a config file, while the self-service portal at /account gives end users password reset and encryption key management. Multi-tenant support with per-tenant quotas enables hosting-platform deployments, and coordinator-less clustering via Zenoh or NATS scales horizontally by adding nodes. Deploy via Docker or the standalone binary. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL v3 licensed.

Mail for your own domain stays on your own server with mailez, a self-hosted stack that delivers over SMTP, IMAP, and POP3 and adds a webmail, calendar, contacts, file storage, and an admin console, all started with a single command. Readers get a draggable three-pane webmail that updates itself over a push channel, merges replies into conversations, folds quoted history, and searches with from:, to:, has:attachment, and date terms. Keyboard shortcuts, a command palette, snooze, scheduled send, undo for bulk moves, and quick reply keep daily mail fast, and the interface installs as an offline-capable app with light and dark themes. Privacy-minded users add PGP signing and encryption, two-factor login, and remote-image blocking, and write server-side rules in a Sieve editor. Calendar, contacts, and Drive sit beside mail, with ICS subscriptions, vCard import, CardDAV and CalDAV sync, and share links. Phones and desktop clients configure themselves through autoconfig. Administrators manage domains, mailboxes, aliases, relays, and external mailbox fetching in one console, generate DKIM keys with a click, and follow a DNS wizard and a health page that verify MX, SPF, DMARC, DKIM, blocklists, and MTA-STS. Audit logs and role-based access keep shared servers accountable. The free community edition runs on a single node, while archiving, DLP, LDAP, ActiveSync, and AI features belong to the paid enterprise edition. 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.

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.

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.

Google Workspace and Microsoft 365, replaced by a platform you actually control: Nextcloud is the self-hosted digital workspace. Files is the core: file storage and sync across desktop, mobile, and web clients, with sharing, versioning, and collaboration built in. Around it, Talk provides private text chat, audio/video conferencing with screen sharing, SIP integration, and persistent voice rooms; Groupware bundles calendar, contacts, and mail with delegation support; and Office offers two collaborative suites - the Collabora-based option with deep ODF support, and Euro-Office, whose local-processing architecture delivers strong Microsoft Office compatibility and fast browser rendering with reduced server load. The Nextcloud Assistant threads AI through the platform via a context-aware sidebar, Whiteboard covers visual collaboration, Flow handles automation, and an app ecosystem of hundreds of extensions adds everything from Kanban boards to end-to-end encryption. Hub 26 brings a lighter UI with a unified app switcher and Nextcloud Governance for organizations under strict regulatory requirements. This is the flagship of data sovereignty: your files, chats, calendars, and documents live on your server, under your jurisdiction, with GDPR compliance by architecture rather than by contract.

A personal cloud does not need the weight of a small enterprise suite, and bewCloud proves it by keeping files, photos, notes, contacts, and calendars in one compact service a single person can run for a whole household. The Files app stores uploads in a plain folder tree on disk, offers public sharing links, optional whole-folder downloads as zip archives, and a WebDAV endpoint that desktop tools can mount. Photos turns that same storage into a browsable gallery, while Notes keeps quick text within reach of every login. Contacts and Calendar speak CardDAV and CalDAV through a bundled Radicale server, so the calendar and address book on a phone or laptop stay in sync without another account anywhere. News collects feeds to read in the browser, and Expenses tracks spending in a small ledger beside everything else. The header shows only the apps you enable, in the order you choose, and companion desktop and mobile apps connect to the same server for people who prefer native sync. Accounts can be protected with multi-factor authentication using TOTP, passkeys, or email codes, and optional single sign-on lets a household sign in through an existing identity provider. 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.

OxiCloud is a self-hosted cloud for files, photos, calendars, contacts, and office documents. Drives can be personal or shared, with configurable storage quotas. Multi-gigabyte uploads travel as parallel, resumable chunks with integrity verification. Images, PDFs, audio tracks, and video streams preview right in the browser, and photos show EXIF details and map locations. Files sync over WebDAV. Calendars sync over CalDAV. Contacts sync over CardDAV. Desktop file managers, Thunderbird, Apple Calendar, and mobile DAVx5 clients connect without proprietary software. Collabora Online or OnlyOffice plug in through WOPI for real-time co-editing of spreadsheets, presentations, and text documents. Administrators enforce role-based access controls. Sign-in runs through OpenID Connect providers such as Keycloak, Authentik, or Azure AD. Public share links can carry a password and an expiration. Identical files are stored once, and adaptive compression keeps footprints compact. Local disks, Amazon S3, and Azure Blob can be mounted at the same time, with live background migration and automated consistency checks. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

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.

Friends drift away when nobody remembers to call; Meerkat CRM is a self-hosted personal CRM that keeps your relationships warm with birthday and stay in touch reminders, contact notes, and a living map of who knows whom. Organize every contact into circles like family, friends, or work, store spouses and children as linked relationships, and see the whole crowd on an interactive network graph that shows how people connect. Sync the same address book two ways: Meerkat runs its own CardDAV server for your phone and can also act as a CardDAV client against an external server you already use. Against each person you can keep the details that matter, dietary habits, kids names, the last conversation, plus a social style timeline of activities you have shared, from dinners to group projects. Reminders nudge you by email when it has been too long, with upcoming birthdays surfaced on the dashboard, so catching up becomes a habit instead of an afterthought. Move data in and out freely: import CSV, VCF, and even a Monica export, export back to CSV and VCF, connect external calendars, and fire webhooks into your own automations. Use it in English, German, Italian, Spanish, or French with light and dark modes, and SSO for whoever shares the house. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Take the tool sales teams use to never forget a client detail and point it at the people who actually matter - friends, family, the colleague whose kid's name you keep blanking on: Monica is a personal CRM. It's a Laravel/PHP application over MySQL where each contact accumulates the texture of a real relationship: how you met, family members and pets, work changes, addresses, notes from conversations, activities done together, gift ideas and gifts given, even debts owed in multiple currencies. Two features set it apart from every contact app. Reminders with staying power: set per-contact intervals (weekly through yearly), get notified at 30 days, 7 days, and day-of, with automatic birthday reminders and CalDAV sync to your calendar. And a journal linked to contacts: write about dinner with friends, tag each person, and build a timeline that's part diary, part relationship log - plus a daily "how was your day" rating. Monica is deliberately manual and deliberately private: no social network features, no AI, no email scraping, no ads, no analytics - a quiet database of what you know about people you love, on your own server. Multiple vaults and users, labels, custom activity types, and document/photo uploads round it out. AGPL-licensed.

CRM mechanics applied to your actual relationships instead of a sales pipeline: Nametag is a Personal Relationship Manager (PRM). It exists to fix the things you keep forgetting: when you last talked to an old friend, their kids' names, the birthday you missed twice. Contacts are tracked with flexible attributes - names, birthdays, important dates, and free-form notes for everything else - and organized into custom groups. Where it goes beyond a contacts app is relationship mapping: you define how people connect to each other (family, friends, colleagues, or custom relationship types), and an interactive D3.js-powered graph renders your entire personal network so you can see clusters and connections at a glance. Staying in touch is automated: scheduled reminders fire for birthdays, important dates, and reach-out nudges, with optional email delivery via a Resend API key for password resets and reminder notifications. Built with Next.js, it is mobile-responsive, ships with full dark mode, and supports multiple languages including English and Spanish. Because it is self-hosted, there are no account tiers or contact limits - unlimited people and relationships, with every note about your personal life stored on your own server rather than a social-graph company's cloud. A lightweight, single-container deployment makes it one of the easiest personal tools to run.