XZip is a clean X Windows interface to games written in Infocom's Z-code
game format. It handles Z-code versions 1 through 5 and version 8. It is
free (yee-ha!)

developed at CMU. Really, I would have preferred to actually do this in
ATK... except that then you'd need ATK to run it, and that's 50 megabytes
of source code. (Honest.) So I just did an imitation.

Z-code games are available at:

ftp://ftp.gmd.de/if-archive/games/infocom/
http://www.edoc.com/zarf/if.html