Z-code file used by the game engine Z-machine, which ran text adventure games in the late 1970s and 80s; commonly run presently by a Z-machine interpreter, several of which have been maintained by community members since the Z-machine was discontinued; contains source code for the games; similar to the Glulx formatted .ULX file extension.

Z-code files use a programming language called the Zork Implementation Language (Zork was Infocom's first game). The file extensions use a numerical value for the version of the Z-machine that is used to run them. Examples include the .Z1, .Z2, .Z3, .Z5, .Z6, .Z7, and .Z8 extensions. Z8 is the most popular extension since it was the last version to be released.