Xinu7

(from Wikipedia)

Xinu ("Xinu Is Not Unix", a recursive acronym) is a Unix-like operating system originally developed by Douglas Comer for instructional purposes at Purdue University in the 1980s. The name is both recursive, and is "Unix" spelled backwards. It has been ported to many hardware platforms, including the DEC LSI-11 and VAX systems, Sun-2 and Sun-3 workstations, Intel x86, PowerPC G3 and MIPS.