The alternatives
Rocket.Chat
The Secure CommsOS™ for mission-critical operations
RocketChat/Rocket.Chat Updated 2026-05-06 Rocket.Chat
The Secure CommsOS™ for mission-critical operations
rocketchat/Rocket.Chat Updated 2026-04-23 mattermost
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
mattermost/mattermost Updated 2026-05-06 zulip
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
zulip/zulip Updated 2026-05-06 element-web
A glossy Matrix collaboration client for the web.
element-hq/element-web Updated 2026-05-05 discussions
Repository for miscellaneous repository management and discussions: https://github.com/revoltchat/revolt/discussions
revoltchat/revolt Updated 2026-02-16 Comparison notes
Rocket.Chat self-hosted replicates most Slack channel and direct message features and supports audio and video calls, but its admin UI is complex and upgrades require careful maintenance planning. Mattermost is more narrowly scoped, targeting developer and DevOps teams with GitLab and GitHub integrations, but lacks Slack's breadth of third-party app integrations and its workflow builder automation. Neither alternative provides a native equivalent to Slack Connect for cross-organization channels — external collaboration requires separate workarounds.
Migration tips
- Export your Slack message history using Slack's workspace data export (available on paid plans) and import into Rocket.Chat using its Slack importer plugin before migrating users.
- Recreate your channel structure in Mattermost or Rocket.Chat before the user migration date to preserve institutional organization patterns.
- Audit your active Slack integrations and identify equivalents — most webhook-based integrations are portable, but Slack OAuth apps with custom flows must be rebuilt against the new platform's API.
FAQ
Can I fully replace Slack with an OSS tool?
Feature parity varies. Most OSS alternatives cover 70-90% of core workflows, but may lack polish, integrations, or specialized features. Pilot the alternative with a subset of your team before fully committing.
What's the cost of self-hosting?
Plan for ~$5-50/month in VPS costs (DigitalOcean, Hetzner, etc.) plus 2-8 hours/month in maintenance. For a team of 20+, self-hosting usually breaks even against SaaS pricing within 6-12 months.
Which alternative should I pick?
Sort by GitHub stars (a proxy for community health), check the last-pushed date (avoid unmaintained projects), and read recent issues to gauge responsiveness.