Rocket.Chat

Rocket.Chat launched in 2015 and has grown into one of the most feature-complete open-source communication platforms available. Its MIT license means the full server — channels, direct messages, voice and video calls, screen sharing, message federation, and end-to-end encrypted rooms — is free to self-host without capability restrictions. With roughly 42,000 GitHub stars it has one of the larger open-source community footprints of any team-chat project.

What sets Rocket.Chat apart from other Slack alternatives is its omnichannel layer. A business can handle internal team messaging and external customer conversations — from WhatsApp, Instagram Direct, email, Facebook Messenger, and live website chat — through a single unified inbox. Agents can be assigned to conversations, SLA timers can be configured, and transcripts can be archived to a central store. That makes it appealing not just as a Slack substitute but as a replacement for standalone live-chat and helpdesk tools.

The technical stack — Node.js and MongoDB on the Meteor framework — is functional but resource-hungry. A small self-hosted instance for 20 users needs at least 2 GB of RAM, and teams running thousands of concurrent users typically provision dedicated infrastructure with horizontal scaling. The admin interface exposes a large number of configuration options, which is powerful but can overwhelm administrators coming from simpler tools. Enterprise features, including advanced omnichannel routing, custom roles with granular permissions, and dedicated support, are available on paid plans starting at $7 per user per month on the cloud offering.