GNU Pth - Portable Threads: portable POSIX/ANSI-C library for Unix gives non-preemptive priority-based scheduling for multithreading in programs. All threads run in same address space
Multi-Threaded Programming with POSIX Threads - Attempts to show how the library's features can be used in "real-life" programs. It explains the different tools defined by the library
Native POSIX Thread Library: NPTL - White paper describes actual implementation of thread library for which requirements are spelled out in a prior document. Many things are different. [Red Hat