Online systems and backends
NativeWebSocket
By endel / Colyseus
WebSocket client for Unity including WebGL, useful for lobby chat and live events with your own server.
Install https://github.com/endel/NativeWebSocket.git#upm-2 through UPM. Create a WebSocket for your ws:// or wss:// endpoint, handle OnMessage/OnError, then call Connect() and SendText(). It exchanges text or binary messages with your server. Do not copy raw source into Unity; WebGL support needs the package's build transformation.
GameSlash reviewed the developer documentation but has not installed or runtime-tested this tool.