EnKai is a library which aims at standardising often used functionality and providing advanced ui elements which the Rift API does not provide. This library is used in all of my updated addons. All of the ui elements you can find in my addons are done using this library.
Within the zip you'll find a readme.odt file. In there is the library documentation. I'll try to keep it updated if the library changes. Currently it's only about halfway done.
Feel free to use this library in your addons. However if you do change the library please send back the changes to me so that I can incoperate them for all potential users.