Xforms
In response to Adam's XForms post
This is one of those standards that was killed by the committee. If you look at the history of it it began in early 2000, and by the time they updated it to use the same data model as XSD schema (2001? 2002?) it looked like it was going to be the NEXT BIG THING, it was going to replace html forms, allow us to capture XML and post it seamlessly to the server blah blah blah...and it IS a really good specification. Unfortunately it took 3.5 years to become a w3c recommendation, that's just too long.
I first looked at it around 2001 and we kept hoping it would become a recommendation, and then some of the major browsers might implement it. Sadly, they didn't and when it did eventually become a recommendation, there was no fanfare as many of the problems it was meant to solve had been solved in other ways, particularly with web services and what is now AJAX. I didn't even know it had become a recommendation at all until I looked at it just now.
It was ahead of it's time, in that murky period when XML was new and all the Schema standards were still finding their feet, before SOAP and XMLHTTPRequest was in it's infancy. It's dead, only Bill could save it now but that seems unlikely.