Synapse

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.