There are two kinds of stackful coroutines - fibers and green threads.

The difference is that fibers stay on the thread they were created on, while green threads can transit between OS threads. There have also been projects to cooperatively schedule OS level threads to minimise latency, but that's a bit different.

I don't know that many decent green thread implementations [off the top of my head], but an interesting one is yahns: https://yhbt.net/yahns/design_notes.txt - to me, green threads have all the benefits of coroutines but all of the downsides of multi-threaded programming.

I implemented fiber based concurrency for C++ here: https://github.com/kurocha/async. An example would be https://github.com/kurocha/async-network/blob/d1d2bf12eb2d9b... - calling read yields the fiber if it would block as implemented here: https://github.com/kurocha/async/blob/2edef4d6990259cc60cc30...

I implemented almost exactly the same model for Ruby here: https://github.com/socketry/async and if you are interested in how it works, see these projects which build on it: https://github.com/socketry/async#see-also