joelsherrill writes: RTEMS (http://www.rtems.org) is a free real-time operating system for embedded systems. The project is celebrating the 21st birthday of RTEMS today. RTEMS supports the single process with filesystem POSIX profile on over a dozen processor architectures. To just be entering young adulthood, RTEMS has had a busy life. It has been a Google Summer of Code project twice (Thanks Google!). It has been to Venus on the Venus Express, circles Mars on the Electra radio, powers Herschel and Planck, is on its way to the asteroid belt aboard DAWN, and has been a key part of physics discoveries at the Stanford Linear Accelerator Center.