Frotz, aside of being an illuminative magic word, is a portable Z-Machine bytecode interpreter - that is, a program for playing games written by Infocom and later games that were compiled with Inform interactive fiction authoring system. It is capable of interpreting code of all Z-Machine versions (Version 1 to Version 8). It was written by Stefan Jokisch.
Great program for playing Zork and the Legion of its descendants...
It supports just about every feature that ever made to Z-Machine.
Frotz has been ported to wide variety of platforms. Some of these versions (MS-DOS, Windows and Amiga versions) also support graphics, mouse and sound. But these platforms are not the only ones! Naturally, UNIX is supported (regrettably with no graphics support whatsoever), as is BeOS, OS/2, RISC OS and even Apple IIgs. It has also been ported to PalmOS, Windows CE and Psion Series 5.
(I just tried the PalmOS version - it rocks. Now, if only I had a keyboard for my Palm, I could have grues in the pocket any day... Install Frotz, use z2pdb to convert storyfiles to .pdbs, hotsync 'em in - and then just play!)
(Also, if you want to play graphical and semigraphical games, such as Zork Zero or Journey or Beyond Zork or whatever in UNIX, I suggest getting UAE, AM1gA ROMz & OSz wAr3z and playing it in emulator. Works great.)
Source code is available, but the licensing says it should NOT be distributed for profit, so it isn't really "open source". It is just Freeware.
You can get Frotz, just like everything else, from the IF Archive (http://www.ifarchive.org/). It is - how could it not? - also available as a Debian package.