By A self-hosted team chat app went open source twelve days ago and immediately hit 791 points on Hacker News. Chatto ships as a single binary, bundles SSO and voice/video calls in its free tier, and implements per-user encryption with crypto-shredding when an account is deleted. If you have been waiting for a Slack replacement you actually own, this is the one worth deploying this week.
One Binary, Zero Infrastructure Tax
Chatto’s biggest practical advantage is what you don’t have to install. The Go backend and Svelte frontend compile into a single executable. NATS for realtime messaging is embedded by default. SQLite handles storage — no PostgreSQL required to get started. TLS provisioning via Let’s Encrypt is built in.
Compare that to Mattermost, which requires PostgreSQL and Redis before you serve a single message, or Rocket.Chat, which needs MongoDB. A Hetzner server at $4–8 per month is enough to run Chatto for a team of fifty. That delta in operational complexity is not a minor detail — it’s the reason teams never finish evaluating Mattermost and stay on Slack for another year.
# macOS/Linux — install via Homebrew
brew install chattocorp/tap/chatto
# Generate configuration
chatto init
# Start the server
chatto serveDocker Compose is available for production setups that need external NATS, Caddy, and LiveKit. Kubernetes manifests are included. For a first deployment, the binary alone is enough. The quick-start documentation covers the full setup in under ten minutes.
Per-User Encryption That Actually Means Something
Most chat apps encrypt data at rest using a single key the server holds. That means the operator — or anyone who gets access to the database — can read everything. Chatto takes a different approach: each user’s messages are encrypted with keys unique to that account.
When a user deletes their account, Chatto performs crypto-shredding: it destroys those per-user keys. A database backup taken ten minutes before deletion cannot recover that user’s plaintext after the keys are gone. The data remains in the backup as encrypted bytes with no corresponding key. This is GDPR’s right to erasure implemented at the cryptographic level, not just a soft-delete flag on a database row. No other major open-source chat application does this by default.
SSO Is Not an Upsell Here
Chatto includes single sign-on, voice calls, video calls, screen sharing, and webhooks in the AGPL license — at no charge. That combination is what the Hacker News thread kept coming back to. Mattermost gates SSO behind its Professional plan at $10 per user per month. Rocket.Chat locks it behind Enterprise. The result is that self-hosted deployments of those tools often launch without SSO because the alternative requires negotiating a contract.
Chatto skips that entirely. SSO works on the day you deploy.
What You Get at v0.4
| Feature | Chatto (free) | Mattermost | Rocket.Chat |
|---|---|---|---|
| SSO | Included | Paid ($10/user/mo) | Paid (Enterprise) |
| Voice/Video | Included | Plugin (paid) | Included |
| Database required | SQLite (no PG day 1) | PostgreSQL | MongoDB |
| Crypto-shredding | Yes | No | No |
| License | AGPL-3.0+ | MIT (core) | MIT (core) |
The current release ships channels, file sharing, reactions, embedded video previews, and configurable roles and permissions. Voice and video calls are end-to-end encrypted with screen sharing included. Binaries are available for Linux (x86_64 and ARM64), macOS, and Windows.
Who Should Deploy Now (And Who Should Wait)
Chatto is the right call for small-to-medium teams leaving Slack over cost, EU companies with data residency requirements under GDPR or NIS2, and any organization that needs account-deletion to be cryptographic rather than contractual. If you already run Docker or a small VPS, the deployment lift is minimal.
It is pre-1.0, currently at v0.4. Breaking changes are possible before the stable release expected in six to twelve months. The AGPL-3.0 license is something commercial teams need to evaluate — though Apache-2.0 exceptions cover the frontend, integrations, documentation, and examples.
If your team depends on Slack’s 1,200+ integrations or needs enterprise audit logs and compliance exports, Chatto is not a replacement today. Come back when v1.0 lands.
What’s Coming Next
ChattoCorp GmbH is building Chatto Cloud — a paid EU-hosted option with fully European infrastructure and no vendor lock-in. You can export and migrate to self-hosted at any time. Cloud regions outside the EU are planned for early 2027. The hosted product is not available yet, but the self-hosted path is production-ready now.
The creator’s open-source announcement is worth reading for the design philosophy. The Linuxiac deployment walkthrough covers the Docker Compose production path. And if you want to track what the community is building with it, the GitHub repository is the place to watch.
