Mercure
Server-sent live updates, protocol and reference implementation
...Mercure is especially useful to add streaming and asynchronous capabilities to REST and GraphQL APIs. Because it is a thin layer on top of HTTP and SSE, Mercure is natively supported by modern web browsers, mobile applications, and IoT devices. A free (as in beer, and as in speech) reference server, as well as a hosted service, are available. Designed for REST and GraphQL. Private updates (JWT authorization). Presence API and subscription events. Event store. Compatible with serverless, PHP, and the like. Supports end-to-end encryption. Reading the documentation is an excellent way to discover Mercure.