Nitfol is a popular interpreter and debugger for the infocom z-machine.
It supports z-machine versions 1 through 8, and complies with version 1 of the Z-machine specification. It uses the GLK libraries to ensure portability to many platforms, including windows and unix.
Some of Nitfol's features include typo-correction, automatic map generation, infinite undo, and a GDB-like source-level debugger. It has been released under the GPL, and can be downloaded from http://www.plover.net/~thumper/nitfol/