7 open source tools compared. Sorted by stars — scroll down for our analysis.
| Tool | Stars | Velocity | Language | License | Score |
|---|---|---|---|---|---|
Rocket.Chat Open source Slack/Teams alternative | 45.0k | — | TypeScript | — | 69 |
Mattermost Open source secure collaboration platform | 36.0k | +100/wk | TypeScript | — | 69 |
Chatwoot Open source live-chat and support desk | 28.0k | +190/wk | Ruby | — | 69 |
discord.js Library for Discord bot development | 26.6k | +22/wk | TypeScript | Apache License 2.0 | 79 |
Zulip Team chat with threading | 24.9k | +49/wk | Python | Apache License 2.0 | 79 |
Synapse Matrix homeserver for decentralized chat | 12.0k | +8/wk | Python | Apache License 2.0 | 79 |
The Lounge Self-hosted modern web IRC client | 6.2k | +13/wk | TypeScript | MIT License | 73 |
Rocket.Chat is self-hosted Slack with Department of Defense certifications. End-to-end encryption, air-gapped deployment, HIPAA compliance — if you need a team chat platform where data never leaves your servers, Rocket.Chat checks every security box. 45k stars and used by government agencies and defense contractors. Mattermost is the developer-focused alternative with better DevOps integrations and a UI that Slack users adapt to instantly. Slack itself is the gold standard for UX but is cloud-only with no self-hosting option. Zulip has a unique topic-threading model that's better for async communication. Use Rocket.Chat if security compliance is non-negotiable — defense, healthcare, government, or any environment requiring air-gapped communication. The catch: the "Other" license is non-standard — commercial features are restricted in the community edition. Self-hosting requires significant resources compared to Mattermost. The UI feels dated compared to Slack and Mattermost. And for teams without strict compliance requirements, Mattermost is easier to deploy, easier to use, and has a smoother Slack migration path.
Mattermost is what you deploy when your company says "we can't use Slack because compliance." It's a self-hosted team chat that looks and feels like Slack circa 2020 — channels, threads, file sharing, integrations — but your data stays on your servers. DevOps and security teams love it. If you're building a startup and need chat without per-seat pricing, Mattermost's free tier is solid for small teams. Slack is the obvious commercial alternative at $7.25+/user/month. Rocket.Chat is another self-hosted option with more features but messier UX. Zulip takes a radically different approach with topic-based threading. The catch: The license changed — it's no longer fully open source. Many useful features (LDAP, advanced permissions, compliance exports) are enterprise-only. And self-hosting means you're the IT department: updates, backups, and uptime are your problem. For most indie hackers, Slack's free tier or Discord is simpler.
Chatwoot is self-hosted Intercom — live chat, email, WhatsApp, social media, all unified in one inbox with an AI assistant (Captain) for automated responses. If Intercom's $39+/seat/month pricing makes your wallet hurt, Chatwoot gives you 90% of the features for the cost of a $10 VPS. For indie hackers who need customer support without per-seat pricing, Chatwoot is the obvious choice. Self-host it and serve 5 or 500 agents for the same infrastructure cost. Crisp is a simpler hosted alternative. Zendesk is the enterprise option at $55/agent/month. Intercom is the gold standard you're trying to avoid paying for. The catch: It's a Rails app, so self-hosting requires Ruby, Postgres, Redis, and Sidekiq — not a trivial stack. The license changed to a custom model, so check the terms. The AI features are basic compared to Intercom's Fin. And "WhatsApp integration" requires a Meta Business API setup that's its own adventure. Budget a weekend for the initial setup.
discord.js is the library that powers most Discord bots in existence. It wraps Discord's API in a clean, event-driven Node.js interface — message handling, slash commands, voice channels, embeds, buttons, and modals all covered. If you're building a Discord bot in JavaScript or TypeScript, discord.js is the default choice. Discord.py is the Python equivalent with a similarly strong community. JDA covers Java. Serenity does it in Rust. Commercially, there's no equivalent — Discord bots are a DIY ecosystem. The library tracks Discord's API changes closely, supports sharding for large bots (1000+ guilds), and the SlashCommandBuilder API makes registering commands straightforward. The catch: Discord's API changes frequently, and breaking changes in discord.js major versions (v13 → v14 → v15) require significant rewrites. The learning curve for voice channels and complex interactions is steeper than basic message bots. Rate limiting is aggressive — your bot will hit it if you're not careful. And you're building on Discord's platform, which means your bot's existence depends on Discord's terms of service and API access policies.
Zulip takes team chat and fixes its biggest problem: finding anything in a wall of messages. Instead of Slack's linear channels where conversations pile on top of each other, Zulip organizes every message into topics within streams. You can catch up on exactly the threads that matter and skip the rest — even days later. For remote-first teams or open-source communities where async communication matters more than real-time banter, Zulip is genuinely better than Slack. The threading model means context survives timezone gaps. Slack is the commercial default everyone knows. Mattermost is the self-hosted Slack clone. Discord's forum channels approximate Zulip's model with a friendlier UI. The catch: Zulip requires discipline — every message needs a topic, and teams that won't adopt that habit will fight the tool constantly. The UI feels academic, not polished. Integrations are fewer than Slack's 2,400+ apps. Video and voice features are basic. And the learning curve turns off teams used to Slack's casual channel vibe. It's objectively better for async work, but adoption is the real challenge.
Synapse is the reference Matrix homeserver — the engine behind decentralized, federated chat that no single company controls. Think email's architecture but for real-time messaging: run your own server, federate with everyone else, own your data. If you want self-hosted team chat with end-to-end encryption and no vendor lock-in, Matrix (via Synapse) is the most complete option. Rocket.Chat is the self-hosted Slack clone — easier to set up but centralized. Mattermost is the enterprise-focused alternative. Commercially, Slack and Teams are what you're replacing. XMPP is the OG federated protocol but the client ecosystem is thin. 115 million addressable accounts across thousands of servers, E2EE by default, and bridges to Slack, Discord, IRC, and more. The Element client is polished enough for daily use. The catch: Synapse is a memory hog. It's Python, and running a homeserver for a busy community can eat gigabytes of RAM. Dendrite (Go) and Conduit (Rust) are lighter alternatives but less feature-complete. Federation means you inherit spam and abuse management complexity. And convincing your team to leave Slack requires genuine motivation — the UX gap, while shrinking, is still real.
The Lounge is a self-hosted IRC client that makes IRC feel modern. It runs as a web app, stays connected when you close the browser (like a bouncer), and the UI looks like it belongs in 2026 rather than 1995. If you're still on IRC — and many open-source communities are — this is how to make it livable. If you want self-hosted IRC with a modern web interface, The Lounge is the best option. Weechat is the terminal-based power user choice. IRCCloud is the commercial hosted alternative with similar always-on functionality. For non-IRC messaging, Matrix/Element, Rocket.Chat, or Mattermost offer self-hosted chat with more features. File sharing, link previews, push notifications, and multi-user support. The setup is a single npm install. MIT licensed. The catch: it's IRC. The protocol is showing its age — no native end-to-end encryption, limited file sharing, no threads, no reactions. The number of active IRC communities is shrinking as teams move to Discord, Matrix, or Slack. The Lounge polishes the experience, but it can't fix the protocol's fundamental limitations. Unless your community is already on IRC, there's little reason to choose it over Matrix or Discord.