★ 45,438TypeScriptNOASSERTIONupdated Jun 2026
best for teams wanting the most mature, feature-complete Slack clone with compliance and video built in
This is the most feature-complete Slack clone on the list. E2E encryption, RBAC, federation, and air-gapped deployment are shipped in the open version, not locked behind an enterprise tier the way Mattermost locks SSO and compliance exports. The Apps-Engine plugin framework sandboxes third-party apps properly instead of just trusting them, which is more than most of the others can claim.
The cost is the stack underneath it. It's 2026 and the core still runs on Meteor.js — the same reactivity model that makes real-time messaging work is also why the build is slow and why hiring for it is harder than for Mattermost's Go/React stack or Zulip's Python. The codebase itself is a visible mid-migration mix of old JavaScript and newer TypeScript.
Expect to run MongoDB, Meteor, and several app instances behind a load balancer before you're anywhere close to HA — this is not the weekend self-host that Mattermost's single-binary pitch promises. Documentation is thorough but split across four separate sites, so finding the right page takes longer than it should.
Our full take →GitHub ↗
★ 37,085TypeScriptNOASSERTIONupdated Jun 2026
best for DevOps-heavy teams who want self-hosted chat wired tightly into their CI/CD and incident tooling
Mattermost is the simplest of the five to get running: one Go binary, Postgres as the only real dependency, and a plugin/webhook ecosystem with 700+ integrations backed by a genuinely serious Cypress-plus-Playwright test suite. If your team lives in CI/CD and incident tooling, the integration surface is the best of the bunch.
The open-core model is the catch. SAML SSO, compliance exports, advanced permissions, and shared channels all sit behind the enterprise license — features Rocket.Chat ships for free in its community edition. You'll feel that wall the moment a real org needs any of them.
The 'single binary' framing also undersells the rest of the stack: file storage, SMTP, and Elasticsearch are all things you'll end up running once search needs to work at scale, and the README doesn't make that obvious. The React frontend is large and historically inconsistent, so onboarding a contributor to it is slower than the backend's simplicity suggests.
Our full take →GitHub ↗
★ 25,355PythonApache-2.0updated Jun 2026
best for async-first teams who want topic-threaded conversations instead of one noisy firehose channel
Zulip is the only one of the five with a genuinely different conversation model. Every message lives in a stream and a topic instead of just a channel, which actually works for async teams instead of just tolerating them the way a Rocket.Chat or Mattermost channel firehose does. 100% mypy coverage and 1500+ contributors mean this isn't a side project coasting on an old architecture.
Self-hosting it is heavier than it looks, though. It wants Ubuntu or Debian specifically, and runs its own Tornado event server alongside Django for websockets — a legacy split that predates modern async Python and adds ops complexity you wouldn't choose today. It doesn't drop into an existing container setup the way Mattermost's single binary does.
Mobile clients are separate repos on their own release cycle, so mobile quality lags the web client — the same blind spot Element has with its own split-off mobile repos. The main repo still carries billing and corporate code, a reminder this was built to run as a hosted SaaS first and self-hosted second; you'll run into that assumption in places you don't expect.
Our full take →GitHub ↗
★ 13,601TypeScriptAGPL-3.0updated Oct 2026
best for orgs that need federated, cross-company chat over the open Matrix protocol
Element is the one app on this list that actually federates. If you need chat across organizations whose servers you don't control, this is the only real option here — Rocket.Chat, Mattermost, Zulip, and Tailchat are all closed gardens, however open their source is. The CI is correspondingly serious: SonarCloud gates and a Playwright suite covering crypto flows and device verification.
That seriousness comes with real weight. This is not something you casually fork — onboarding means reading several docs before you're productive, and browser support explicitly deprioritizes anything outside the latest Chrome, Firefox, Edge, and Safari. That's a problem if you're in one of the older enterprise environments that otherwise makes Rocket.Chat or Mattermost the obvious pick.
Mobile is pushed off to separate element-x-android/ios repos, so this README tells you almost nothing about the mobile experience you'd actually ship. Federation is the whole reason to pick this over the Slack clones; if you don't need it, you're paying a lot of complexity for a feature you won't use.
Our full take →GitHub ↗
★ 3,635TypeScriptApache-2.0updated Oct 2026
best for small teams wanting the lightest self-hosted footprint of the bunch
Tailchat is the lightest thing here by a wide margin. The microkernel frontend and microservice backend are a real design choice, not a buzzword — there's an actual CLI with generator templates for scaffolding plugins, and CI includes nightly Vercel deploys plus Docker canary builds. Next to Rocket.Chat or Element, this feels like an app you could read in an afternoon.
That lightness shows up as real gaps. There's no federation or interoperability with Matrix, XMPP, or ActivityPub — odd for a project that markets itself against walled gardens, since that's exactly what you're left running yourself. The plugin interface is explicitly unstable (the docs use the phrase 'Break Change'), and a leftover client/desktop-old directory sitting next to the current one suggests an unfinished migration.
At 3.6k stars against Rocket.Chat's 45k, it's also a fraction of the size and maturity of everything else on this page. Fine for a small team that wants something simple to run without four docs sites to read first; risky if you expect the plugin ecosystem or compliance tooling the bigger projects have built over years.
Our full take →GitHub ↗
// questions people ask
Before you choose
Which one is easiest to actually self-host?
Mattermost, on paper — it's a single Go binary with Postgres as the only hard dependency, versus Rocket.Chat's MongoDB-plus-Meteor stack or Zulip's Ubuntu-only install with a Django/Tornado split. In practice you'll still need file storage, SMTP, and Elasticsearch for real search, so budget more than the 'single binary' pitch implies.
Which is best for a regulated or compliance-heavy team?
Rocket.Chat, mainly because E2E encryption, RBAC, and air-gapped deployment ship in the open version rather than behind a paywall. Mattermost has the same ambitions but gates SSO and compliance exports behind its enterprise license, so you'll hit that wall sooner than expected.
Do I actually need Matrix and Element instead of a Slack clone?
Only if you need to chat with people outside your organization's own server — Element is the one app here that federates over an open protocol. Rocket.Chat, Mattermost, Zulip, and Tailchat are all closed gardens you run for your own team, which is simpler if cross-org federation isn't a real requirement.
What should a small team with limited ops capacity pick?
Tailchat has the lightest footprint by far and the easiest deploy story of the five. The tradeoff is a much smaller project — 3.6k stars against Rocket.Chat's 45k — with an unstable plugin API and no federation, so it fits a small team fine but won't grow with you the way the bigger projects will.
If you want this kind of judgment without doing the digging yourself, that's basically what the finds.dev weekly email does — a short list of repos picked for what you actually care about, with the actual weaknesses included.