wxwidgets

This nomination is from Chris Bruner. It was suggested after the Wikimedia Foundation suggestion, 2007-11-09

UPDATE: Chris says that he is okay with this being his first nomination, before Wikimedia.

Chris writes:

It's one of these behind the scenes opensource projects, that I don't think gets much support, but is very useful. It is a cross platform widget maker that is in use in several applications

The donation link is on the main page. http://www.wxwidgets.org