What is the difference between Mattermost and Slack Connect?

Mattermost is best for Teams that need self-hosted, privacy-first messaging, while Slack Connect is best for Organizations needing secure inter-company messaging. Mattermost starts at Free (self-hosted) and Slack Connect starts at $7.25/user/mo.

Is Mattermost or Slack Connect cheaper?

Mattermost starts at Free (self-hosted) and is free. Slack Connect starts at $7.25/user/mo.

Is there a free alternative to Slack Connect?

Yes, Mattermost offers a free tier.

Mattermost vs Slack Connect

Mattermost is open-source, self-hosted team messaging platform for organizations that need data sovereignty, while Slack Connect is slack feature for connecting channels between different organizations securely. The biggest difference up front: Mattermost is free, while Slack Connect starts at $7.25/user/mo. Mattermost is built for teams that need self-hosted, privacy-first messaging, whereas Slack Connect targets organizations needing secure inter-company messaging.

At a glance

	Mattermost	Slack Connect
Best for	Teams that need self-hosted, privacy-first messaging	Organizations needing secure inter-company messaging
Starting price	Free (self-hosted)	$7.25/user/mo
Free tier	✓	—
Open source	✓	—
Free tier available	✓	—
Open source	✓	—
Channels	✓	—
Compliance	✓	—
Cross-Org Channels	—	✓
DMs	—	✓
Integrations	✓	—
Playbooks	✓	—
Security	—	✓
Self-Hosted	✓	—
Workflows	—	✓

Mattermost

Strengths

Self-hosted — full control over your data
Open source with active community
Slack-compatible interface, easy migration
Strong compliance and security features

Weaknesses

Requires server management if self-hosting
Smaller integration ecosystem than Slack
Cloud-hosted version is more expensive than Slack
Mobile apps lag behind Slack and Teams in polish

Try Mattermost → Full review

Slack Connect

Strengths

Cross-organization channels let you collaborate with external partners in shared spaces
Includes Security as a core feature, purpose-built for team communication workflows
Affordable at $7.25/user/mo — one of the lower-priced options in the team communication category
Includes dms alongside the core feature set — fewer separate tools needed

Weaknesses

No free plan — you need to pay $7.25/user/mo from day one to use it
Fewer built-in features means you may need additional tools to cover gaps
Notification overload is a real problem as the number of channels grows
Relatively new (founded 2020) — the feature set and integrations are still maturing

Try Slack Connect → Full review

The bottom line

Pricing: Mattermost is completely free, which makes it the obvious pick if budget is the top concern. Slack Connect starts at $7.25/user/mo. That cost buys you a more polished or feature-rich experience, so it comes down to whether the extras justify the spend.

Feature gaps: Mattermost offers Channels, Compliance and Integrations that Slack Connect lacks. Slack Connect brings Cross-Org Channels, DMs and Security that Mattermost does not have.

Team fit: Both tools target mid-size teams teams, so the decision hinges on features and workflow fit rather than scale.

Open source: Mattermost is open source, meaning you can self-host, audit the code, and avoid vendor lock-in. Slack Connect is proprietary — you are trusting the vendor with your data and uptime.

Where each tool shines: Mattermost's biggest strengths are: self-hosted — full control over your data. open source with active community. Slack Connect's biggest strengths are: cross-organization channels let you collaborate with external partners in shared spaces. includes security as a core feature, purpose-built for team communication workflows.

Watch out for: With Mattermost, users commonly note that requires server management if self-hosting. With Slack Connect, the main complaint is that no free plan — you need to pay $7.25/user/mo from day one to use it.

Choose Mattermost if...

Your profile matches its sweet spot: teams that need self-hosted, privacy-first messaging
Budget is a hard constraint — Mattermost is free, Slack Connect is not
You need self-hosting, data sovereignty, or the ability to audit source code
You specifically need Channels and Compliance
You care about open source with active community

Choose Slack Connect if...

Your profile matches its sweet spot: organizations needing secure inter-company messaging
You specifically need Cross-Org Channels and DMs
You care about includes security as a core feature, purpose-built for team communication workflows