

Zork is one of the most popular text-adventures and one of the first interactive fiction games ever created. The first Zork was developed in the seventies and ported on various platform by Infocom in the early 80s. Infocom was one of the most prolific developers of text-adventures for home computers and created memorable interactive fiction games; Zork was perhaps their most popular one.
The Hitchhiker's Guide to the Galaxy is a humorous free text adventure game based on the novel of the same name written by Douglas Adams (if you never read it, shame on you!). The Hitchhiker's Guide to the Galaxy was designed by Douglas Adams himself and interactive fiction god Steve Eric Meretzky, it was released by Infocom in 1984 for DOS and for Macintosh.
Bureaucracy is an abandoned text-adventure game designed by Douglas Adams (yes, the writer of The Hitchhiker Guide of the Galaxy), developed and published by Infocom in 1987. Bureaucracy is a peculiar interactive fiction; the game challenges you to solve frustrating bureaucratic problems in a world populated by strange characters.
Mines of Titan (also known as Mars Saga for other platforms) is an abandoned single-player RPG with a sci-fi setting (you're going to Mars!). Mines of Titan was developed by Westwood Studios and released by Infocom in 1989 for DOS, Apple II and Commodore 64.
Circuit's Edge is a single-player science fiction blend of adventure game and RPG, developed by Westwood Studios and released by Infocom in 1990. Circuit's Edge is based on George Alec Effinger's cyberpunk novel "When Gravity Fails".