3 Best Open-Source Alternatives to Mattermost in 2026
By Noahlast updated pricing verified
Compared: open-source alternatives to Mattermost
| Alternative | Best for | Standout | Biggest weakness | Learning curve | Price |
|---|---|---|---|---|---|
| Mattermostreference | regulated, government, or defense organizations that need self-hosted, air-gapped, or sovereign-cloud team chat with compliance controls a SaaS-only tool like Slack can't provide | Deployment flexibility for compliance-sensitive organizations: the same platform can run fully air-gapped or in a sovereign cloud with FIPS 140-3/STIG-hardened compliance options, not available from mainstream SaaS chat tools. | No paid tier publishes flat per-user pricing; Professional, Enterprise, and Enterprise Advanced all require a sales conversation and prepaid annual seat commitment, making it harder to budget or compare cost against competitors up front, and self-hosting the free core requires ongoing server maintenance. | Moderate | Free |
| Rocket.Chat | regulated and security-conscious organizations (government, defense, healthcare, financial services) that need a self-hostable or air-gapped team chat platform, plus teams wanting a free, open-source Slack alternative | A fully open-source (MIT-licensed), self-hosted Community Edition with no user limit, alongside government and defense deployment options authorized up to DoD Impact Level 6 for classified environments. | None of the paid tiers publish list pricing — Commercial, Government, and Defense plans all require contacting sales for a quote, making it hard to budget or compare costs against competitors like Slack or Mattermost without a sales call. | Moderate | Free |
| Zulip | distributed and remote teams, open-source projects, and research groups who need many parallel conversations to stay organized without a flat, scrolling chat feed | Topic-based threading splits every channel into named sub-conversations by default, so a team can hold dozens of parallel discussions in one channel without losing track of any of them, and the full self-hosted edition is genuinely free with no per-user cap on core features. | Topic-based threading is a real behavior change from flat-stream chat apps like Slack or Microsoft Teams, so teams migrating over often need a deliberate adjustment period, and self-hosting requires the same ongoing server maintenance any self-hosted Basic/Business/Enterprise pricing. | Moderate | Free tier · paid from $3.50/mo |
| Element | government, defense, and enterprise organizations that need self-hosted, end-to-end encrypted chat with the option to federate across organizational boundaries | Matrix federation lets a self-hosted Element server exchange encrypted messages with users on entirely different organizations' servers, something closed platforms like Slack or Teams cannot do. | Enterprise and Sovereign pricing is not published; both require a sales conversation, and Enterprise pricing only applies from a 100-user minimum, making Element's paid tiers impractical to evaluate cost for small teams. | Moderate | Free |
Mattermost
Rocket.Chat
Zulip
Element1.Rocket.Chat — best Mattermost alternative for regulated and security-conscious organizations (government, defense, healthcare, financial services) that need a self-hostable or air-gapped team chat platform, plus teams wanting a free, open-source Slack alternative
Rocket.Chat is the best Mattermost alternative for teams that want a fully open-source, self-hostable chat platform with no per-tier commercial license split, unlike Mattermost's open-core model where advanced features (sovereign AI, high availability, air-gapped support) sit behind a separate commercial Enterprise license. Rocket.Chat's Community edition is entirely MIT-licensed, free, self-hosted, and unlimited on user count, matching Mattermost's own free self-hosted core, and its GitHub repository has more than 46,000 stars, ahead of Mattermost's nearly 39,000. Rocket.Chat also supports deployments authorized up to DoD Impact Level 6 on its Defense tier, a depth of government and defense deployment comparable to Mattermost's own FIPS 140-3/STIG-hardened Enterprise Advanced options. Rocket.Chat holds a 4.3/5 rating from 156 Capterra reviews, a smaller sample than Slack's but more third-party evidence than Mattermost's single 5/5 Product Hunt review. Mattermost is still the better choice for buyers who want built-in Microsoft Teams interoperability and Kanban-style playbook automation, features Rocket.Chat doesn't list, and for organizations that value Mattermost's public roster of named enterprise customers (NASA, Samsung, the U.S. Air Force) as a compliance reference; Rocket.Chat's Commercial, Government, and Defense tiers all require the same sales-quote process Mattermost's paid tiers do, so neither product is more price-transparent than the other.
Compared to Mattermost: MIT-licensed Community edition with no separate commercial-license split vs Mattermost's open-core Enterprise license gate, 46,000+ GitHub stars vs nearly 39,000, Defense tier authorized up to DoD Impact Level 6
Wins:Community edition is entirely MIT-licensed with no advanced features gated behind a separate commercial license, unlike Mattermost's open-core split · GitHub repository has more than 46,000 stars vs Mattermost's nearly 39,000 · Defense tier supports deployments authorized up to DoD Impact Level 6
Loses:No built-in Microsoft Teams interoperability or Kanban-style playbook automation the way Mattermost lists · No published roster of named enterprise customers (Mattermost cites NASA, Samsung, and the U.S. Air Force) · Commercial, Government, and Defense tiers all require a sales quote, same as Mattermost's paid tiers
Pros
- Community Edition is free, open-source (MIT license), and self-hostable with no user limit.
- Deployment options span standard cloud hosting to fully air-gapped, classified environments.
- Federated communications let separate Rocket.Chat deployments message across organizational boundaries.
- Extensible via custom and pre-built apps, plus native voice, video, and screen sharing.
Cons
- No published list pricing for any paid tier; every quote requires a sales conversation.
- Self-hosting the Community Edition adds administration and infrastructure overhead compared to SaaS competitors.
- Government/Defense-specific features add complexity that most mainstream business customers won't need.
Pricing: Free — Both free self-hosted cores cost $0 with no user cap; neither product publishes paid-tier dollar pricing (verified undefined NaN, NaN)
2.Zulip — best Mattermost alternative for distributed and remote teams, open-source projects, and research groups who need many parallel conversations to stay organized without a flat, scrolling chat feed
Zulip is the best Mattermost alternative for distributed teams that want topic-based threading — splitting every channel into named sub-conversations by default — rather than Mattermost's flat channel-and-thread model. Zulip's self-hosted edition is free with the complete feature set and no per-user cap, matching Mattermost's free MIT-licensed core, and its source is published on GitHub (zulip/zulip, 25,700+ stars) under the Apache 2.0 license. Zulip holds a 4.9/5 rating from 196 Capterra reviews, the highest score among Mattermost's listed alternatives and far more third-party evidence than Mattermost's own single 5/5 Product Hunt review. Zulip Cloud also publishes flat per-user pricing — Standard at $6.67/month billed annually ($8/month billed monthly) and Plus at $10/month billed annually — where none of Mattermost's three paid tiers show a dollar figure. Mattermost is still the better choice for organizations that need government-grade compliance certifications and sovereign or air-gapped deployment: Zulip's pricing and feature set target distributed teams and open-source projects rather than regulated government and defense buyers, and it doesn't advertise FIPS 140-3/STIG-hardened compliance or named customers like NASA and the U.S. Air Force the way Mattermost does. Teams migrating from Mattermost's flat-channel model to Zulip's topic-based threading also face a real adjustment period, per Zulip's own listing.
Compared to Mattermost: free self-hosted core with no per-user cap on both, 4.9/5 rating from 196 reviews vs a single Product Hunt review, published Cloud pricing from $6.67/month vs no public price
Wins:Topic-based threading organizes many parallel conversations within one channel, a different model from Mattermost's flat channels · 4.9/5 rating from 196 Capterra reviews, the highest score among Mattermost's listed alternatives · Zulip Cloud publishes flat per-user pricing from $6.67/month billed annually, while none of Mattermost's three paid tiers show a dollar figure
Loses:No advertised FIPS 140-3/STIG-hardened compliance or named government customers like Mattermost's NASA and U.S. Air Force references · Topic-based threading is a real behavior change from flat-channel chat, requiring a genuine adjustment period for switching teams · Positioned toward distributed teams and open-source projects rather than regulated government and defense deployments
Pros
- Self-hosted edition is fully open source (Apache 2.0) and free with the complete feature set and no user cap.
- Topic-based threading keeps many parallel conversations organized within a single channel.
- Cloud Free plan includes hundreds of integrations and guest accounts, not just a stripped demo.
- Apps available on web, Windows, macOS, Linux, iOS, and Android.
Cons
- Topic-based threading is a different mental model from flat-stream chat and requires teams to adjust their habits.
- Cloud Free caps search history at 10,000 messages, which active teams can hit quickly.
- Cloud Plus and Self-Hosted Business both carry 10- and 25-user minimums, respectively, so small teams pay a per-seat floor.
- Self-hosting requires ongoing server maintenance to get the same reliability as the managed Zulip Cloud.
Pricing: Free tier · paid from $3.50/mo — Zulip Cloud Standard at $6.67/month billed annually vs Mattermost's contact-sales-only Professional tier with no published price; both self-hosted free tiers are $0 (verified undefined NaN, NaN)
3.Element — best Mattermost alternative for government, defense, and enterprise organizations that need self-hosted, end-to-end encrypted chat with the option to federate across organizational boundaries
Element is the best Mattermost alternative for organizations that need encrypted messaging that can federate across separate companies' servers, something Mattermost's centralized deployment model doesn't support. Element is built on Matrix, an open, decentralized protocol, so a self-hosted Element/Matrix homeserver can still exchange end-to-end encrypted messages with users on an entirely different organization's server, unlike Mattermost's self-contained, single-organization deployments. Element's Community edition is free and AGPL-3.0-licensed for self-hosting, comparable to Mattermost's own free MIT-licensed core, and its Sovereign tier supports fully air-gapped, offline-capable installs for government and defense customers, matching the depth of Mattermost's FIPS 140-3/STIG-hardened Enterprise Advanced tier. Element counts NATO, UN agencies, and several European governments and militaries among its users, a similar regulated-sector customer base to Mattermost's own NASA and U.S. Air Force references. Mattermost is still the better choice for buyers who want a lower entry point for paid features: Element's Enterprise tier only becomes available from a 100-user minimum, a higher floor than any of Mattermost's tiers state, and neither Element's Enterprise nor Sovereign pricing is published, matching Mattermost's own lack of published paid-tier pricing, so cost comparison for either product requires a sales call. Element also carries no external ratings on Capterra, Product Hunt, or G2, versus Mattermost's own single Product Hunt score.
Compared to Mattermost: Matrix federation lets self-hosted servers message across organizations, Sovereign tier matches FIPS 140-3/STIG-hardened compliance depth, Enterprise tier requires a 100-user minimum
Wins:Matrix federation lets a self-hosted Element server exchange encrypted messages with users on entirely different organizations' servers, which Mattermost's centralized model doesn't support · Sovereign tier supports fully air-gapped, offline-capable installs, matching Mattermost's FIPS 140-3/STIG-hardened Enterprise Advanced depth · Named regulated-sector customers include NATO, UN agencies, and several European governments and militaries
Loses:Enterprise tier only becomes available from a 100-user minimum, a higher floor than any Mattermost tier states · Neither Enterprise nor Sovereign pricing is published, matching Mattermost's own lack of published paid-tier pricing · Carries no external ratings on Capterra, Product Hunt, or G2, versus Mattermost's single Product Hunt score
Pros
- Matrix federation allows cross-organization encrypted messaging without shared infrastructure.
- Community edition is fully free and AGPL-licensed for self-hosting.
- Sovereign tier supports fully air-gapped deployments with no internet dependency.
- Native apps cover web, Windows, macOS, Linux, iOS, and Android.
Cons
- Enterprise and Sovereign pricing is not published; both require contacting sales.
- Enterprise tier only becomes available from a 100-user minimum, limiting its use for small teams.
- Self-hosting the Community edition requires running and maintaining your own Synapse homeserver.
- The dual AGPL/commercial licensing model can be confusing for organizations unsure which terms apply to their use case.
Pricing: Free — Both free self-hosted cores cost $0; neither Element's Enterprise/Sovereign nor Mattermost's Professional/Enterprise/Enterprise Advanced tiers publish a dollar figure (verified undefined NaN, NaN)