Game playing on computers dates back to some of the earliest machines. The game spacewar which was normally a two player graphical shoot the other spaceship game was first written for the PDP1 in 1962. I first ran across the game as a commercial arcade game in the late 70's before I got interested in PDP8's. A good description of the origin of the game is in a Creative Computing Article . I have a copy of the game but it requires the VC8E point plot display which doesn't have a web interface yet.
A good description of the later popularity of the game among computer people is an article from Rolling Stone .
Many other classic games were available for the PDP8. I have a copy of Adventure and a Start Trek based game that you can run among others. See shortcuts menu for the easy way to run the games and help on online games.
See Images for information on some of the disk images with games