In 1985, Mark J. Welch designed the Generic Adventure Game System (GAGS), a computer programming tool for creating "text adventure" games for MS-DOS computers. GAGS was released as "shareware" in 1985 and enhanced several times in 1986 and 1987.
In 1987, David Malmberg made substantial enhancements to the Generic Adventure Game System, which was renamed the Adventure Game Toolkit (AGT). Over the next few years, many additional features were added to AGT, and versions were released for MS-DOS, Microsoft Windows, the Apple Macintosh, the Commodore Amiga, and the Atari ST. From 1987 through 1992, AGT was distributed by Softworks of Mission San Jose, California. The final version of AGT, known as the "Adventure Game Toolkit Master's Edition," includes some graphics and sound capabilities. The final version of AGT is version 1.7.
More than 100 differnt text adventure games have been designed by game authors around the world using GAGS and AGT, and more than 80 of those games are available for downloading from the "Interactive Fiction Archive." (ftp://ftp.gmd.de/if-archive/). GAGS and AGT games are available in several different directories there, in both source code and compiled versions.
Rather than just downloading dozens of games in hopes of finding some good ones, I suggest that you check out Baf's Guide to the Interactive Fiction Archive, which includes reviews of many dozens oftext adventure games, including many AGT games.
Since 1993, the Generic Adventure Game System and the Adventure Game Toolkit have been released as "freeware" (e.g. they are still copyrighted, but may be freely copied and distributed in unaltered form); no registration fee is requested. Freeware is not public domain: you may not distributed altered versions or source code, or use the "Adventure Game Toolkit" product name, without written permission from Mark Welch or David Malmberg! No technical support is available from the authors. David Malmberg has moved from Mission San Jose, California to southern California, where he works for a software distribution company. Mark J. Welch is now an attorney in Pleasanton, California.
At least two people have been working on enhanced adventure-game-writing tools that will be backward-compatible with earlier AGT source code:
Those interested in text adventure games should explore XYZZY News, a bi-monthly newsletter available on the Internet. In addition, text adventure game fans are active in the "Gamer's Forum" on CompuServe.
Finally, perhaps the best resource for text-adventure-game designers is the newsgroup rec.arts.int-fiction, where users of a wide variety of gamewriting systems come together to discuss their art. My suggestion, before accessing the newsgroups directly, is to search for recent discussion threads by subject using Alta Vista or DejaNews (search for "AGT" or "Super AGT" or "Portable AGT").