blackadder from the kompany is looking to fill this niche as well. 
right now you can download the beta* version for $50, which includes a
qt forms editor and some other niceties.

* - the current version seems to be broken with a "packaging issue,"
which seems to be a bum rpm on rh linux, at least.  After much
knashing of teeth I got it to work, entirely against it's will.  The
Ruby support just doesn't look to be there for Qt (the main reason I
was so excited about this product) and, in general the ruby support
seems tacked on at the moment.  Message to the kompany: please deliver
-- this stuff will be very cool when it works.