The GNU Portable Threads

 Pth is a very portable POSIX/ANSI-C based library for Unix platforms which
 provides non-preemptive priority-based scheduling for multiple threads of
 execution ("multithreading") inside server applications. All threads run in the
 same address space of the server application, but each thread has its own
 individual program-counter, run-time stack, signal mask and errno variable.