I miss mozilla's XUL language (and XBL!), those were awesome.
My company, me as a solo dev, back in 2003-04 built a "single page app" using XUL and iframes. Still has some 200 monthly users, the poor bastards. They have to download Firefox 3.6 iirc, and it only works in an 800x600 window.
XUL was beastly back then though.
Seems like a comment comes up about XUL every few years and I can't help but be sniped by it. A xulrunner app was my first job out of college in '08, good memories, fun dev environment!