Microsoft Excel is a commercial spreadsheet program made by Microsoft that is part of their office suite. As spreadsheets are often useful things for GemStone III, especially with their ability to compute formulas and such, there are several spreadsheets that one can download and use with the game.
There isn't that much here on this page yet, but there is more to come -- provided that people start sending in their spreadsheets.
Elfarran's Character Trainer - Calculates stat growth, MTP/PTP, AS, DS, CS, TD, allows you to plan your skill and spell training, and much much more. The original version of this calculates up to 28 levels (any range of levels will do, either 0-27 or 100-127). I also have released my own modified verseion that goes up to 50 levels in advance.