I'd like to share that we've just released Centrifugo v6 - a major update of scalable WebSocket server. The release addresses some usability pain points and adds nice features and more observability.
Centrifugo is an open-source standalone server written in Go – https://github.com/centrifugal/centrifugo. Centrifugo can instantly deliver messages to application online users connected over supported transports (WebSocket, HTTP-streaming, Server-Sent Events (EventSource), GRPC, WebTransport). Centrifugo has the concept of a channel – so it's a user-facing PUB/SUB server. Everything implemented in a language-agnostic way – so Centrifugo can be used in combination with any frontend or backend stack.
These days we also provide Centrifugo PRO version – and trying to find a balance to be sustainable.
The server is based on the open-source Centrifuge library - https://github.com/centrifugal/centrifuge, so many improvements mentioned in Centrifugo v6 release blog post (even those for Centrifugo PRO) may be used just as a library in Go application.
We provide real-time SDKs for popular client environments – for browser and mobile development – they connect to both Centrifuge library based servers and Centrifugo server.
Generally Centrifugal ecosystem provides a good alternative to Socket.IO and cloud services like Pusher.com and Ably.com
Will be happy to answer on any questions