Well, I would guess you can't do this under the
GSL, if you are going to use the license. Going ahead without the license is possible ...
The problem is, do you have the time and money to have a good IP lawyer review your software/web-based product in order to make sure you are clearly in "fair use" territory? I think it has been mentioned in some other posts (might be on another board-I have only skimmed some of the threads). Fair Use and what exactly falls under fair use is somewhat murky. It would require knowledgeable legal advice to insure you don't step where you shouldn't and, let's face it, that would be a huge expense to do properly. This is pretty much why anyone publishing material for
4e is going to use the
GSL.
In addition, if you do it wrong and get sued,
WotC can step forward and show the court how they created a license allowing FREE use of their IP to create compatible products. That would undoubtedly be a major point in their favor.
Software products like character generators, etc. are specifically forbidden by the
GSL. If you want to go that route, you'll have to stick to "fair use." Personally, I would, um, let someone else do it.
Patrick