Self-Hosted Chat & Communication

Slack-shape (team chat, channels, threads)

• ★ Mattermost — most polished Slack alternative; channels, threads, integrations, slash commands; mobile + desktop apps. Default for businesses self-hosting.
  • https://github.com/mattermost/mattermost
• ★ Rocket.Chat — feature-rich; multi-protocol bridges; many integrations; can feel heavy.
  • https://github.com/RocketChat/Rocket.Chat
• Zulip — threaded-by-default; great for async-first teams; loved by OSS projects.
  • https://github.com/zulip/zulip

Matrix / federated

• ★ Synapse (Element) — the reference Matrix homeserver; mature; federation; bridges to everything.
  • https://github.com/element-hq/synapse
• Conduit / Conduwuit — Rust Matrix homeserver; lighter than Synapse.
  • https://gitlab.com/famedly/conduit
• Dendrite — Go Matrix homeserver; alternative to Synapse.
  • https://github.com/element-hq/dendrite
• Element — the leading Matrix client; web / desktop / mobile.
  • https://github.com/element-hq/element-web

Discord-shape (voice + channels + servers)

• ★ Revolt — open-source Discord alternative; growing community.
  • https://github.com/revoltchat/revolt
• Mattermost also handles voice/video calls.

Video / voice meetings

• ★ Jitsi — see Realtime Video for the broader space.
  • https://github.com/jitsi/jitsi-meet
• BigBlueButton — designed for online classrooms; powerful.
  • https://github.com/bigbluebutton/bigbluebutton
• MiroTalk — lightweight WebRTC.
  • https://github.com/miroslavpejic85/mirotalk
• LiveKit Server — production-grade SFU; see Realtime Video.

Federated alternatives to Twitter / Reddit / etc.

• Mastodon — Twitter-shape federated.
  • https://github.com/mastodon/mastodon
• Lemmy — Reddit-shape federated.
  • https://github.com/LemmyNet/lemmy
• Pixelfed — Instagram-shape.
  • https://github.com/pixelfed/pixelfed
• PeerTube — YouTube-shape.
  • https://github.com/Chocobozzz/PeerTube

Newsletters / mailing

• Listmonk — newsletter platform; Go; self-host.
  • https://github.com/knadh/listmonk
• Postal — full mail server.
  • https://github.com/postalserver/postal

Support / live chat (homelab side)

• See Customer Support for Chatwoot / Plain / Crisp.

Bridges (connect Matrix to Slack / Discord / etc.)

• mautrix- family — bridges for WhatsApp, Telegram, Signal, Discord, Slack, iMessage, etc.
  • https://github.com/mautrix
• matterbridge — multi-network bridge; not Matrix-specific.
  • https://github.com/42wim/matterbridge
• t2bot.io / Beeper — hosted Matrix bridge sets.

Patterns to adopt

• ★ Pick Mattermost or Matrix. Mattermost for "we're a team and want Slack." Matrix for "we want federation + bridges + privacy."
• Federation matters or it doesn't. Be honest with yourself; Matrix has real ops cost.
• Mobile apps are the test. If your team won't install the mobile app, you've lost.
• Backup the DB. Chat history is hard to reproduce.
• Bridges are best-effort. Production-grade SLO over a Matrix-Discord bridge is wishful thinking.

Pick this if…

• Default self-host team chat: Mattermost.
• Federation / bridges to many networks: Matrix Synapse.
• Threaded async-first: Zulip.
• Discord-shape community: Revolt.
• Online classrooms / education: BigBlueButton.
• Newsletter: Listmonk.