Research Unix Version 7 has been ported to the Raspberry Pi:
It seems to run both in emulation (via qemu) and on the actual hardware. It is single-core (unsurprisingly!) on the multi-core Pi hardware, and it appears to be mostly early V7 (there is some mention of backports of better malloc and printf. It would be interesting to see some of the BSD 2.x tools ported over, and perhaps a TCP/IP stack.