Not sure if you're only considering Unix/BSD-ish OSes here or not. But there are perhaps hundreds of such projects. http://tunes.org/cliki/operating_20systems.

Not sure if you're only considering Unix/BSD-ish OSes here or not. But there are perhaps hundreds of such projects. http://tunes.org/cliki/operating_20systems.html http://tunes.org/cliki/operating_20systems.html You may want to dig around that entire site to get an idea of what people have tried to do (and frequently failed).