This is an External AddOn that modifies the looks of Tukui without direct editing.
ShifteUI is an AddOn that external edits the code of Tukui which is an extreme light-weight user interface for World of Warcraft dedicated to replace the one provided by Blizzard.
The external edit allows for users to download Tukui directly from the Tukui site and update Tukui as they get updated without having to worry about losing anything from this AddOn, or having to wait (or wait as much as before) for the 'edit' to be updated accordingly.
This AddOn is designed for 1680 or greater resolution, and World of Warcraft. Anything lower and this AddOn may not function optimally.