I was bored so I thought I would make a list of operating systems that are available on the web Some are well known and others you may have never heard of. Most descriptions of the Operating Systems are on their web site
http://www.e-smith.org/ A Linux distribution that acts like a full server and gateway
http://www.knopper.net/knoppix/index-en.html Runs on a large number of hardware configurations, boots in under two minutes and is adaptable.
http://www.ibiblio.org/peanut/ Small but packed and nice looking Linux distribution, only 210 Mb download installs to 600 Mb on your harddisk.
http://tiny.seul.org/en/ Tiny Linux is a small Linux distribution designed especially for old recycled computers
Other free Unix Operating Systems
Educational Operating Systems