Haiku Project
BeOS (the OS Haiku is a reimplemntation of) has an interesting history. It was an OS that has a fully async C++ API (very novel for it's time and even now). The fact that it was async made the OS much more responsive and had a better CPU utilization.<p>BeOS was another company that Apple considered to purchase but they ended up buying NeXT instead. IIRC they ended up going with NeXT because BeOS didn't have networking back then.