Apout Uses So Far

Runs binaries from 5th, 6th, 7th Edition Unix
Runs binaries from 2.9BSD and 2.11BSD
Runs binaries from 1st & 2nd Edition Unix
 even though the underlying OS has been lost
Earliest C compiler source code (1972 to 1973)
 can compile these & then self-compile.
Remember: source is useless unless you can compile and run it 8-)