OpenSwap

Slack alternatives

3 projects that cover part or all of what Slack does. 3 of them have an open-source core; 0 are source-available; 0 need a human license read.

Pl. 01
OPEN CORE

Mattermost

replaces Slack

Source under AGPLv3 (OSI) or a commercial licence; compiled binaries MIT, admin tools Apache 2.0; Enterprise parts licensed separately

★ 40kunratedpush 2026-11-10

Pl. 02
OPEN CORE

Rocket.Chat

replaces Slack

MIT core; apps/meteor/ee and ee/ are under a proprietary licence

★ 46kunratedpush 2026-11-10

Pl. 03
OPEN SOURCE

Zulip

replaces Slack

Apache-2.0 (OSI-approved, whole repository)

★ 26kunratedpush 2026-11-09

What does it cost?

Slack price: $7.25 per user per month (Pro plan, billed annually). Pro $7.25/user/mo billed annually ($8.75 monthly); Business+ $15/user/mo billed annually ($18 monthly). Source: vendor pricing page, checked 2026-11-10. Vendor site: Slack site. Put your plan's price into the estimator below if it differs.

Example values: replace every number with your own. SaaS price prefilled from Slack pricing, checked 2026-11-10; the other numbers are examples.

Self-hosting saves about $120 a year for 20 seats: SaaS $1,740 vs self-host $1,620 (server $144, backups $36, admin time $1,440). Break-even at about 19 seats at these numbers.

Functions differ: an open-source tool rarely matches every Slack feature. Self-hosting means you handle updates, backups and security. Sponsored plate: none yet. Advertise.