Earth, a FrameXML library, is useful for rapidly creating Frames in WoW.

By using Earth, it is possible to create a fancy quest log rather quickly, for example.

Screenshot 1 shows the minimap-Icon which opens a configframe shown in screenshot 2. Though not directly related to Earth, this shows two possibilities to use the Earth library.

API documentation (not yet done, but links to useful tutorials):
http://www.wowwiki.com/Earth

Note: This is the extracted Earth-folder from Cosmos. I provide this for people who like to use this addon but do not like to use the complete Cosmos compilation.
I'm not related to the developer (Alexander Brazie) who codes Earth.