The Original Guidebook, maintained by Andrew Williams, started as simple ASCII, but has been expanded to take advantage of the more advanced features that HTML offers. However it currently bans information gained via code diving. The Improved Guidebook on the other hand, besides improved interface, structure and navigation, has been expanded to include all available information, code diving not excluded. The reason for existence of the IGB is to have a SINGLE, unrestricted and complete ADOM reference.
Most recently, all of the info from Sorear's Wiki has been incorporated.
The HTML compilation is available for download and offline reference. The most recent version of these documents will always be found zipped on the main website, adomgb.sweb.cz. The online reference, currently updated at 24 hour intervals, can be found at lonkero.eu/igb or natrox.org/adom/improved. Please report any error or inaccuracy you find to pmencik at seznam dot cz; type "IGB" in the subject line.
These documents are always under construction relative to ADOM 1.1.1. The historical work on the Guidebook was done by the Usenet newsgroup rec.games.roguelike.adom (Google Groups) but nowadays most players frequent official forums at Thomas Biskup's ADOM site.