Shameless plug: if you're looking for something a little more full-featured but maybe not quite as small, take a look at Kitten <a href="https://software.sandia.gov/trac/kitten" rel="nofollow">https://software.sandia.gov/trac/kitten</a>. It's still a minimal OS (LWK: lightweight kernel), but it has thinks like.. disks and networking.