Inform is a
programming language created by Graham Nelson specifically for
writing Interactive Fiction. Historically, Inform has been the most popular language for writing standard (non-adult) Interactive Fiction. For whatever reason, it hasn't been quite as popular for writing AIF.
Version 7 of Inform, released in early 2006, adds some significant new capabilities and a very user-friendly game-authoring toolset. Some AIF authors have already begun to create libraries in Inform 7, and it will be interesting to see whether this new version catches on as a language for writing AIF.
If you have specific questions about programming in
Inform, the best place to go is rec.arts.int-fiction.
Inform 7 - The official home page for Inform 7
inform7aif - A Yahoo group for discussion of writing AIF in Inform 7. The files section includes some AIF libraries written in Inform.
Simple Sex - Alpha release of AIF libraries for Inform 7, by Gareth. These are available for testing purposes and probably contain bugs.