A really good entry to the International Obsfucated C Code Contest.
This entry, by Christopher Mills - PDP-7/11 simulator, won the Best of Show in 2018. Here are the notes:
The program delivered here is both a full machine emulation of the original PDP-7 that Ken Thompson used to write the first version of UNIX and a full machine emulation of the PDP-11/40 used by subsequent UNIXes. The Makefile can build versions that can run each of the following:
1. UNIX v0 for the PDP-7 (circa 1969) 2. Research UNIX Version 6 (circa 1975) 3. BSD 2.9 (circa 1983)