libpcrt
libpcrt is a lightweight library that implements POSIX threads' interface with pure user-level multithreading supported by the setcontext family. By preloading this library, applications could benefit from user-level thread switching without any modification.
Building
A single make is adequate. Build options are defined in common.h:
DEBUG: undefine it to turn off logging.
Usage
LD_PRELOAD=/path/to/libpcrt.so [original command]