event-loop

Neither amphp or reactphp will let you start running blocking functions in parallel out of the box. They basically just provide syntactic sugar for making single-threaded, cooperative multitasking easier by wrapping php's native ability to read/write to sockets asynchronously (or by using pecl extensions.) So you can respond to websocket messages or http requests asynchronously but you're not going to be able to implement anything like a parallel merge sort were you offload work to other threads. Things like general purpose file IO are not easy at the moment either. Amphp might seem a heavy handed because they've taken the monorepo approach. ReactPHP on the other hand has broken everything up into individual components. For example, you can get started with ReactPHP by just pulling in the event loop https://github.com/reactphp/event-loop.