AntimatterCompare
Antimatter vs Slack
Slack is the best-known team chat. It runs only in Slack's cloud, and much of it is behind paid plans.
Why teams choose Antimatter
- Your messages and files stay on your own servers, and the whole server is open source.
- Everything is included: no per-seat price, no SSO tax, no message history limit, no paid AI add-on.
- Voice channels, whiteboards and notes come built in, and AI works with your own models.
When Slack may suit you better
- You don't want to run a server at all.
- You rely on apps from Slack's large directory that have no Antimatter or Mattermost equivalent.
- You work with many outside organisations that are already on Slack.
Feature by feature
| Feature | Antimatter | Slack |
|---|---|---|
| Hosting and licensing | ||
| Self-hosted on your own servers | ✓ Yes | ✕ No |
| Open-source server | ✓ YesAGPL v3 | ✕ No |
| Every feature without a paid plan | ✓ Yes | ✕ No |
| Runs offline, without internet access | ✓ Yes | ✕ No |
| Messaging | ||
| Channels, direct messages and threads | ✓ Yes | ✓ Yes |
| Unlimited message history | ✓ Yes | ◐ Partlylimited on the free plan |
| Scheduled messages and reminders | ✓ Yes | ✓ Yes |
| Message priority and acknowledgements | ✓ Yes | ✕ No |
| Self-destructing (burn-on-read) messages | ✓ Yes | ✕ No |
| Automatic translation of channels | ✓ Yesself-hosted models | ✕ No |
| Calls | ||
| Voice and video calls with screen sharing | ✓ Yes | ◐ Partly1:1 only on the free plan |
| Always-open voice channels | ✓ Yes | ◐ Partlyhuddles |
| Live captions and call transcripts | ✓ Yesyour own speech-to-text | ◐ Partlypaid plans |
| Apps and AI | ||
| Collaborative notes and documents | ✓ Yes | ✓ Yescanvases |
| Whiteboards | ✓ Yes | ✕ No |
| Kanban boards | ✓ Yes | ◐ Partlylists |
| Incident and process checklists | ✓ Yes | ◐ Partlyworkflows |
| Polls | ✓ Yes | ◐ Partlythrough apps |
| AI assistants with the models you choose, self-hosted included | ✓ Yes | ◐ Partlypaid add-on, vendor models |
| Security and administration | ||
| Single sign-on (SAML, OpenID Connect) | ✓ Yes | ◐ Partlypaid plans |
| LDAP and Active Directory sync | ✓ Yes | ✕ No |
| Data retention and compliance export | ✓ Yes | ◐ PartlyEnterprise |
| Federation with other servers | ✓ Yesshared channels | ◐ PartlySlack Connect, paid plans |
| End-to-end encryption of messages | ✕ No | ✕ No |
"Partly" means the feature needs a paid plan, an add-on or a plugin, or exists in a limited form; the note says which. Based on each product's public documentation as of October 2026: plans and features change, so check the vendor's own site before deciding. Spotted a mistake? Tell us.