Darwin

From Wikipedia:

Darwin was a programming game invented in August 1961 by Victor A. Vyssotsky, Robert Morris Sr., and M. Douglas McIlroy. The game was developed at Bell Labs, and played on an IBM 7090 mainframe there. The game was only played for a few weeks before Morris developed an “ultimate” program that eventually brought the game to an end, as no-one managed to produce anything that could defeat it.