What is the best open-source alternative to Slack?

The best open-source alternative to Slack is Mattermost, which features Developer Integrations and is optimized for DevOps & Security Teams. Other notable options include Zulip, Rocket.Chat, Matrix / Element.

Is there a free self-hosted alternative to Slack?

Yes! Self-hosted options like Mattermost and Zulip and Rocket.Chat and Matrix / Element are completely free to run on your own servers and bypass commercial licensing fees.

Communication & Marketing

Best Slack Alternatives

Slack is a fantastic tool, but its pricing escalates dramatically for larger teams, and data history constraints on the free tier push teams toward self-hosting.

About Slack

Pricing: $8.75/user/monthOfficial Website

Direct Feature Comparison

Software Name	Free Plan	Open Source	Self Hosted	Key Feature	Best For	Link
Target SL Slack	✓	✗	✗	Mainstream Suite	Universal Standard	Visit
MA Mattermost	✓	✓	✓	Developer Integrations	DevOps & Security Teams	Visit
ZU Zulip	✓	✓	✓	Threaded Asynchronous UI	Asynchronous Remote Teams	Visit
RO Rocket.Chat	✓	✓	✓	Omnichannel Support	Customer-facing Orgs	Visit
ME Matrix / Element	✓	✓	✓	Decentralized / E2EE	High Privacy Teams	Visit
DI Discord	✓	✗	✗	Voice Channels / Huddles	Communities & Tech Startups	Visit

Top 5 Alternatives Reviewed

Structured overview of the strongest replacement choices

Mattermost

Free (Self-hosted)

#01

A secure, open-source collaborative communication platform built for technical teams.

Best For: DevOps & Security TeamsKey Feature: Developer Integrations

Free PlanYes

Open SourceYes

Self HostedYes

Visit Website

Zulip

Free / $6.67 cloud

#02

An open-source chat application optimized for asynchronous, organized thread discussions.

Best For: Asynchronous Remote TeamsKey Feature: Threaded Asynchronous UI

Free PlanYes

Open SourceYes

Self HostedYes

Visit Website

Rocket.Chat

Free (Self-hosted)

#03

An open-source hub for team communications and customer support chats.

Best For: Customer-facing OrgsKey Feature: Omnichannel Support

Free PlanYes

Open SourceYes

Self HostedYes

Visit Website

Matrix / Element

Free (Open Protocol)

#04

An open, encrypted, decentralized standard protocol for secure, real-time communications.

Best For: High Privacy TeamsKey Feature: Decentralized / E2EE

Free PlanYes

Open SourceYes

Self HostedYes

Visit Website

Discord

Free (Ad-supported features)

#05

A popular chat, voice, and community platform that has become widely adopted by startups.

Best For: Communities & Tech StartupsKey Feature: Voice Channels / Huddles

Free PlanYes

Open SourceNo

Self HostedNo

Visit Website

🔓 Open-Source Options

Mattermost: Open code base built for DevOps & Security Teams. Features developer integrations.
Zulip: Open code base built for Asynchronous Remote Teams. Features threaded asynchronous ui.
Rocket.Chat: Open code base built for Customer-facing Orgs. Features omnichannel support.
Matrix / Element: Open code base built for High Privacy Teams. Features decentralized / e2ee.

🖥️ Self-Hosted Options

Mattermost: Run locally or on custom cloud VMs. Ideal for devops & security teams.
Zulip: Run locally or on custom cloud VMs. Ideal for asynchronous remote teams.
Rocket.Chat: Run locally or on custom cloud VMs. Ideal for customer-facing orgs.
Matrix / Element: Run locally or on custom cloud VMs. Ideal for high privacy teams.

💡 Final Recommendation

If you prioritize threaded asynchronous discussions, **Zulip** is revolutionary. For secure enterprise collaboration and compliance, **Mattermost** is the strongest alternative.