Comparisons anchored on Mattermost, the open-core team chat platform, against other self-hosted Slack replacements.
Two open-core Slack replacements: Mattermost's Go binary on PostgreSQL with HA and air-gapped deployment in paid plans against Rocket.Chat on MongoDB with a free 50-user Starter plan. Verdict by user count, compliance needs and which features each puts behind a subscription.
A single-vendor chat platform or a federated protocol: Mattermost against Matrix with the Synapse homeserver and Element clients, compared on federation with outside organizations, AGPL licensing, SSO through Matrix Authentication Service, bridges and operating effort.
The three-way shortlist for self-hosted secure messaging in government and regulated teams: licensing and paid tiers, databases, federation, SSO and air-gapped options side by side, with a pick by scenario.
What each charges for: Mattermost's Professional, Enterprise and Enterprise Advanced seat subscriptions against Rocket.Chat's free Starter and Community limits and quoted paid plans, mapped to SSO, HA, audit and air-gapped needs, plus the self-hosting costs that apply either way.
Which Mattermost build and plan a self-hosted chat deployment should run: the MIT Team Edition without SSO, the free Entry mode of Enterprise Edition with its message history cap, or a Professional, Enterprise or Enterprise Advanced subscription for SSO, compliance exports, high availability and air-gapped operation.
The three self-hosted Slack replacements most teams shortlist: open-core Mattermost, Rocket.Chat with its MIT core and enterprise directories, and Apache-2.0 Zulip with topic threading and no open-core split. Compares which SSO and compliance features need a paid plan, mobile push limits, release support windows, imports between them and running costs.
Channel-based chat against topic-threaded chat: Mattermost versus Apache-2.0 Zulip, whose self-hosted server includes SAML, LDAP and SCIM without an open-core split. Compares paid plans, mobile push limits, compliance features, imports and operating effort.
A dedicated team chat platform against chat inside Nextcloud: channels, integrations and compliance features against Talk's file and calendar integration and calls, with what each needs to scale and which plan unlocks SSO.
Running team chat with no internet: Mattermost's air-gapped deployment in Enterprise Advanced against Rocket.Chat's requirement for a Starter or premium license and offline registration, plus certificates, push notifications and the FOSS build route.
The Operator with S3-compatible storage and a managed database against a single Linux binary with PostgreSQL: plan requirements, file storage rules for high availability, upgrades and the team size where Kubernetes pays off.
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