Zork: The Undiscovered Underground
is a text-adventure game
released for free by Activision in 1997 as a prequel and promotional item for their upcoming graphical adventure Zork: Grand Inquisitor
It was written by former Infocom
"Implementors" Mark Blank and Michael Berlyn.
Since it was written in the Inform
programming language, it can be run on any platform that supports a Z-Machine Interpreter