XForms is one of those things I'd heard of, but hadn't really paid much attention to. I've had a chance lately to dive into it a little and there are some very interesting ideas. This tutorial article will tell you a little about it and more about its recalculation algorithm. The summary is that XForms defines a spreadsheet-like calculation capability and cleanly separates data from presentation. It's too early to know whether or not it will ever go mainstream, but I think that its ideas will have impact regardless.