GAGS - The Generic Adventure Game System, by Mark J. Welch. GAGS is the predecessor of AGT (q.v.); GAGS game files can be run with GAGS or compiled and run with AGT.
GAGS, version 1.06B, comes as a DOS package containing DOS executables for the game interpreter and editor, and the source code for a sample game (Underground adventure). The documentation is also available.