Free operating system for Atari computers, and more.
EmuTOS is a TOS compatible operating system for Atari ST series computers, and more. It is made from Digital Research's GPLed original sources and is a free and open source alternative to Atari proprietary ROMs.
Blueport is an italian Open Source 32-bit operating system ... This project has temporarly moved to Gna.org: <a href="http://gna.org/projects/blueport">Blueport project</a>
tOfuS is an OS kernel with framework capabilities, in order for everyone to experiment on it. (was: A Music-Production oriented Operating System, for use in recording studios and live performances as a mixing desk and user-programmable DSP).