Open Source Chat
Chat software carries more weight than its casual interface suggests: for a team it becomes the unofficial record of every decision and handoff, and for a private conversation it is the one place metadata like who talked to whom can leak. The catch is that chat covers at least three different tools - an internal team workspace, an end-to-end encrypted messenger, and a public community platform - and the right pick depends on which one you actually need. Open source lets you keep the message history in a database you run, read how the encryption and federation actually work rather than trust a claim, and avoid a per-seat invoice on the place your people think out loud.
Discourse
Open-source community discussion platform with self-hosting, built-in chat, and themes
Rocket.Chat
Open source team communications platform with messaging, voice, video, federation, and apps
LibreChat
Self-hosted AI chat platform with model switching, agents, MCP, and multi-user access
Mattermost
Open source self-hosted collaboration platform with chat, workflow automation, voice, and screen sharing
Chatwoot
Open-source customer support platform for live chat, email, and omnichannel inboxes
Jitsi Meet
Open source video conferencing for browsers, mobile apps, self-hosted servers, and embedded meetings
Huly
Open-source team platform combining project management, chat, CRM, HRM, and applicant tracking
Zulip
Open source team chat with topic-based threading for live and asynchronous conversations
SimpleX Chat
Private messenger with no user IDs, link or QR based connections, and double ratchet end to end encryption
Our picks
Three servers stand out for internal team chat; a fourth covers the privacy-first case.
Best self-hosted team chat: Mattermost Mattermost runs as a single Linux binary over PostgreSQL and ships a monthly MIT-licensed build covering chat, workflow automation, voice, and screen sharing. It exposes APIs, webhooks, slash commands, and plugins, with clients for web, mobile, and every desktop OS, so it slots into an engineering team's tooling. Self-hosting covers Docker, Kubernetes, and Linux packages.
Best for asynchronous teams: Zulip Zulip's defining feature is topic-based threading: messages live in a channel and then a named topic, so distributed teams follow only the threads they care about. It is built for both live and asynchronous conversation, self-hosts on Ubuntu, Debian, or Docker, and is Apache-2.0 licensed. Choose it when your team spans time zones.
Best all-in-one communications platform: Rocket.Chat Rocket.Chat combines messaging, voice, video, and federation with role and attribute-based access control and optional end-to-end encryption. A marketplace and the Apps-Engine let you install or build integrations, and it runs self-hosted, in the cloud, or air-gapped via Docker, Podman, or Kubernetes. It fits teams that also talk with external customers.
Best for private, metadata-light messaging: SimpleX Chat SimpleX Chat has no user IDs at all - you connect by sharing a link or scanning a QR code. Messages use double ratchet end-to-end encryption with an extra layer, and you can run your own relay servers, which store messages only until delivery. It suits sensitive small-group talk rather than a company knowledge base.
Decide what kind of conversation you are hosting
Three very different products hide under the word chat, and picking the wrong one is the usual first mistake. A team workspace like Mattermost, Rocket.Chat, or Zulip is built around persistent rooms, searchable history, and integrations with the rest of your tools. A private messenger like Session, SimpleX Chat, or Jami optimizes for metadata protection and encryption, usually giving up central administration and long-term history to get there. A community platform like Discourse is really a public forum with chat attached. Match the tool to how your group talks before comparing features, because a messenger built for privacy makes a poor company knowledge base.
For a team server, retention and identity matter as much as the chat window, because the history quietly becomes a record system. Look at whether you can set retention by room, whether deleted messages are truly gone, and whether administrators can read content. End-to-end encryption protects sensitive rooms but changes search, moderation, and bot access, so decide where you actually need it; Rocket.Chat and Mattermost both offer it without forcing it on every channel. If single sign-on through SSO or LDAP is required, test it before rollout rather than after, since directory integration is where migrations stall.
Then pressure-test the parts users feel every day: reliable desktop clients, mobile push notifications, unread counts, mentions, and file handling. For engineering teams, webhooks, bot APIs, and slash commands often matter more than visual polish - Mattermost and Zulip both expose deep APIs, and Zulip's topic-based threading suits asynchronous work across time zones. Finally, check the exit before you enter: confirm messages, users, channels, uploads, and reactions can be exported in a usable format, because a chat system with weak migration tooling gets sticky faster than you expect.
Related categories
Frequently asked questions
Team chat, private messenger, or community platform - which do I need?+
They solve different problems. Team workspaces like Mattermost, Rocket.Chat, and Zulip center on persistent rooms, history, and integrations for internal collaboration. Private messengers like SimpleX Chat and Session prioritize encryption and metadata protection for sensitive one-to-one and small-group talk. Community platforms like Discourse host public discussion. Naming which of these you actually need first saves you from judging a tool on the wrong criteria.
How does end-to-end encryption change how a chat server works?+
It protects message content from the server, but it affects search, moderation, compliance review, bot access, and account recovery. Some systems encrypt only direct messages; Rocket.Chat and Mattermost support encrypted rooms while leaving other channels searchable. Test device enrollment, lost-device recovery, and whether search still works before relying on it. Strong privacy only helps if people can still operate the system day to day.
Will the mobile apps and push notifications actually be reliable?+
Mobile is where self-hosted chat most often disappoints, so check it early. Confirm the project has maintained iOS and Android clients, and understand how push is delivered, since some self-hosted deployments need extra gateway setup to route notifications. Rocket.Chat, Mattermost, and Zulip all ship first-party mobile apps. Test mentions, muted rooms, background sync, and attachments on a real device before you commit a team.
Does federation matter for my team?+
Federation lets separate organizations talk while each keeps its own server and rules. That is valuable across a real administrative boundary and unnecessary for a single company that only needs internal rooms, where it adds identity-trust, moderation, and delivery complexity. Rocket.Chat supports federation if you need cross-org messaging. If your problem is internal collaboration, a simpler single-server model is easier to run and easier for users to understand.
Which integrations should I weigh most heavily?+
Prioritize the ones that match your workflow over a long connector count. Webhooks, bot APIs, OAuth, and slash commands usually matter more than a big catalog, and engineering teams often need issue-tracker, CI, and monitoring alerts routed into rooms. Mattermost lists a large marketplace and Rocket.Chat has its Apps-Engine for custom apps. Also check permission boundaries so a bot cannot read more rooms or data than it needs.
Is there an open source option for customer support or Discord-style communities?+
Yes, and they are different tools from team chat. Chatwoot is a self-hosted support platform that pulls live chat, email, and social messages into one shared inbox with agent workflows. For Discord-style servers and channels, Stoat and Spacebar reimplement that model on infrastructure you control, with Spacebar aiming for compatibility with existing Discord clients and bots. Match the tool to the audience: staff, customers, or a community.
What should I check about importing existing chat history?+
Migration difficulty depends on what your current system exports. Basic messages and users usually transfer, but threads, reactions, edits, files, private channels, and timestamps often need cleanup, and identity mapping is the hardest part when usernames or emails changed over time. Run a trial import with real data into a test instance before announcing a cutover date, and verify that attachments and private rooms survived.