ZZT is not mainly used for RPG's, in fact, there haven't been any ZZT RPG's out for a while. ZZT can be used for a mix of things including Action, Adventure, Dungeon Crawls, Side-Scrollers, and pretty much anything if you have enough creativity. The graphics of the games you can make are bad. Take a look at the screenshot and you will know what I mean (sorry for the bad one, click here for an enlarged version).
You can find a lot of games and tips from other ZZT-fans at the
ZZT website. Take a look at it, there are really much ZZT-games!