RTEMS (Real-Time Executive for Multiprocessor Systems) is a free real-time operating system (RTOS) designed for deeply embedded systems such as automobile electronics, robotic controllers, and on-board satellite instruments.

RTEMS is free open source software that supports multi-processor systems for over a dozen CPU architectures and over 150 specific system boards. In addition, RTEMS is designed to support embedded applications with the most stringent real-time requirements while being compatible with open standards such as POSIX. RTEMS includes optional functional features such as TCP/IP and file systems while still offering minimum executable sizes under 20 KB in useful configurations.

The RTEMS Project is the collection of individuals, companies, universities, and research institutions that collectively maintain and enhance the RTEMS software base. As a community, we are proud to be popular in the space application software and experimental physics communities. RTEMS has been to Venus, circles Mars, is aboard Curiosity, is in the asteroid belt, is on its way to Jupiter, and soon will circle the sun. It is in use in many high energy physics research labs around the world. There are many RTEMS users who do not belong to the space or physics communities, but our small part in contributing to basic scientific knowledge makes us proud.