Quetzal
From Just Solve the File Format Problem
Quetzal is a saved-game format for Z-code and Glulx games.
It was devised for Z-code in 1997 by Martin Frost, and was universally adopted shortly thereafter. (Prior to its adoption, every Z-code interpreter, including Infocom's, used its own format for saved games, and they were not formally specified or interoperable.)
The same basic format was re-used by the later Glulx virtual machine (circa 1999). The specification for the Glulx VM describes how Quetzal usage differs for Glulx.
It is an IFF-based format (FORM IFZS). There isn't a widely-used conventional filename extension.
