The BSD family tree
Heh. Between NetBSD 1.4 and Darwin/Mac OS X there's an entry that just says "(?)".<p>It's probably pretty well-known that question mark is NeXTSTEP, which was built at NeXT, the company that Steve Jobs founded after he left Apple the first time around. NeXTSTEP was built around BSD mostly because of Avie Tevanian's involvement in CMU's Mach kernel project.