A key advantage of fibers of course is that they preserve exception semantics, whereas tame can't in all cases. I'm not too interested in reviving the stalemated thread v. event religious war. I prefer explicitly-managed events, but if others prefer a more thread-like API, by all means....
In the end, both are the same thing; managing action-specific state in an application-defined per-action data structure. With OS threads, you let the OS manage the state instead. This can be inefficient with a large number of actions, because most of the state kept has nothing to do with the application itself; it's OS bookkeeping overhead.
