Glulx

Description
Glulx is a story file format for Interactive Fiction games. It is developed and maintained by Andrew Plotkin. The purpose of Glulx is to eliminate some limitations of the original Z-code Z-machine format, most notably the file size limit. Glulx files may be stand-alone or they may be included in a Blorb archive. The standard file extension for a Glulx file is .ulx.

Resources
Glulx IFWiki entry