Linux on a 286?
Linux is a multi-user, multitasking operating system which requires a 386 processor or more to run. This is because the lower PC processors don't have what is needed for the Linux kernel.
Linux being open source, is being ported to many architectures. And one group decided to modify the kernel so it would run on a 286 processor. The project page is http://www.uk.linux.org/ELKS-Home/index.html.