The coroutines are regular threads. The library provides an interface for syncing which makes them behave as if they were "real" coroutines. This avoids common problems you run into when making coroutines in C++ which by itself does not support coroutines natively - but it supports threads very well.
Pros: Very easy to implement and use. Will likely work very well anywhere without much thought.
Cons: Resource hungry. Not really designed for thousands of simultaneous coroutines.
It's really nice for scripting things as you can tests a bunch of conditions, yield() and then re-test without needing to build an explicit state machine. Much easier for designers to grok.
Usually done in Lua, which is a fantastic language for gamedev(low overhead, fast, coroutine support and integrates very nicely with C/C++).
It still requites a syscall and the entities being scheduled are proper kernel level threads.
So not really fibers. Pretty cool though.
Edit: autocorrect
By the way, I found barriers to be very simple to work with for some rough multithreading. Just line all the threads up, then let them go.