The Hitchhiker's Guide to the Galaxy - The Adventure Game 
This game rocks! It's a text adventure, much like Zork! or one fo those types of games, but it's been updated with a few graphics and put up on the Web for all of us to play. It was originally created in 1984 from a collaboration between Douglas Adams and Steve Meretzky of Infocom. In it's prime it was one of the best selling video games, selling more than 350,000 copies. But now it's free and you should play it. The Hitchhiker's Guide to the Galaxy is awesome. But be warned, it's extremely difficult, save often, and you might need a few hints along the way. I've made it about 70 turns and I'm completely stumped, but I'll figure it out sooner or later. Enjoy!