OSI-licensed only · self-hostable
PubNub is a hosted real-time messaging platform: publish and subscribe channels, presence and push delivered over a global network. It is proprietary, billed by usage. Open-source replacements give you the same publish/subscribe model on your own servers, but you run the infrastructure and handle scaling yourself.
Every tool below is under an OSI-approved licence (Apache-2.0, MIT or AGPL-3.0), checked against its repository. EMQX, a popular MQTT broker, moved to the Business Source License and is listed separately at the end.
Licences checked against each repository on November 7, 2026.
| Tool | Best for | Licence | Runs as |
|---|---|---|---|
| Centrifugo | Closest drop-in real-time messaging server | Apache-2.0 | Docker |
| Socket.IO | Bidirectional events inside a Node.js app | MIT | Server |
| Mercure | Server-sent events for live updates | AGPL-3.0 | Server |
| NATS | Backend messaging between services | Apache-2.0 | Server |
| Supabase Realtime | Postgres changes and ephemeral messages | Apache-2.0 | Server |
| Soketi | Pusher-compatible WebSockets | AGPL-3.0 | Docker |
Best for: Closest drop-in real-time messaging server
An open-source scalable real-time messaging server. Clients connect over WebSocket and other transports and subscribe to channels while your backend publishes through an API.
Best for: Bidirectional events inside a Node.js app
Bidirectional, low-latency communication for every platform. A library with client and server components, including rooms for grouping connections.
Best for: Server-sent events for live updates
A protocol for pushing live updates to browsers and other HTTP clients, with a free reference hub written in Go. The managed hub on mercure.rocks is a separate paid service.
Best for: Backend messaging between services
A simple, secure and performant communications system for digital systems, services and devices. Strong for service-to-service messaging; browser clients typically connect through its WebSocket support.
Best for: Postgres changes and ephemeral messages
Sends ephemeral messages, tracks and synchronises shared state, and listens to Postgres changes over WebSockets.
Best for: Pusher-compatible WebSockets
A next-gen, Pusher-compatible, open-source WebSockets server. Useful if your clients already speak the Pusher protocol.
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| If you need… | Start with |
|---|---|
| A standalone pub/sub server with channels | Centrifugo |
| Real-time events in a Node.js app | Socket.IO |
| One-way live updates over HTTP | Mercure |
| Messaging between backend services | NATS |
| Realtime on a Postgres-based stack | Supabase Realtime |
| Existing Pusher clients | Soketi |
Public source code, but under licences the Open Source Initiative doesn't approve. Fine to use; read the terms first.
Source is public, but since version 5.9.0 the project moved from Apache-2.0 to BSL 1.1, and multi-node clusters need a licence file. BSL is not an OSI-approved licence.
Quick answers to common questions
Yes. Centrifugo (Apache-2.0) is a standalone real-time messaging server with channel subscriptions, and is the closest open-source analogue. Socket.IO, NATS and others cover different parts of the same job.
All six tools here are self-hostable. Centrifugo, Mercure and Soketi are deployed as servers or containers; Socket.IO is embedded into your own application.
Not any more. The repository states that from version 5.9.0 it uses the Business Source License 1.1, which is not OSI-approved.
Supabase Realtime lists tracking and synchronising shared state among its features. Check each project's docs for presence support before committing to one.
You take on scaling, monitoring and uptime yourself. PubNub's managed global network has no direct open-source equivalent, so plan capacity for peak connection counts.
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