The interface is heavily (well, completely) based on ATK, an X toolkit 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.
Here is a screen shot of XZip (monochrome GIF image, 11K).
It is running Graham Nelson's excellent text game Curses! (also freeware, but not distributed by me.) Note the scroll bar, full-justified text, boldface, full mouse and keyboard text editing, and Emacs-style key bindings. (Ok, the Emacs keys are harder to see.) On a color display, you can also customize the window and text colors.
The Z-code engine in XZip is taken from ZIP V2.0.7 by Mark Howell (howell_ma@movies.enet.dec.com).
You can download the source code. It's a tarred, compressed file, about 136K. It should build easily on any Unix platform with X windows (including Linux.)
John Elliott (jce@seasip.demon.co.uk) has provided a source code patch which adds support for the Beyond Zork graphical font. The patch includes a BDF font file.
If you like the XZip interface, you may also be interested in MaxZip, a similar interpreter I wrote for the Macintosh. There's also MaxTADS, an interpreter for playing TADS game files on the Macintosh.
Here is the directory of Z-code games in the IF Archive.
I myself have written several games in Z-code format. People seem to think that some of them are pretty good.