there seem to be a crop of php developers discovering the value of xul. the intro is a little over the top, but it’s a nice entry-level article:

“Here’s a question: what if I was to tell you that you can write your own version of Word using something like HTML and JavaScript? What if I added that you could run on your hard disk or launch it directly from your Web server and use it to update your site’s content? It sounds a little far fetched, I know, but it’s right here, right now — and it calls itself “Zool”.”