I ran across an interesting assembly-based 64-bit operating system that may prove useful to real-time robotics systems on a broad standards-based scale. It may or may not be useful (you know, the usual caveat about "new" stuff), but it would be very educational for anyone in Computer/Electrical Engineering or Computer Science to poke around with.
Personally I'd like to poke around with some sensor processing via software filters, yet I'm sure there are other applications (like image processing, or GPGPU integration) that may also be useful.
http://www.returninfinity.com/baremetal.html
You can start it with a virtual machine -- QEMU is shown in their screenshots but my personal favorite for ease of use in Windows is
VirtualBox. This assumes you have a 64-bit processor that also supports hardware virtualization -- many CPU's do, yet you may have to turn it on in the BIOS.