AceGUI

AceGUI is a development tool to make it easy to develop GUI's. Here is a link to its post in the wowace forums.

Oh, and I think it may be obvious, but this does require Ace.

[2006-06-20] 0.9.1
- Updated toc for 1.11
- Fixed issues with Button's text introduced in 1.11

[2005-12-04] 0.090
- Enhanced support for FontStrings
- Dropdown bug fixed
- Added more events to several controls
- Reverted version number down to 0.090
- Added support for ClearAllPoints to be done before anchors are applied