Robo GUI is a beautiful Sci-Fi GUI skin for Unity.
The skin's API is scripted in C#.
The skin contains a custom window system which simplifies everything.
The window background is stretchable without losing quality.
The windows are made to fade in/out on open/close.
The skin contains many custom elements such as:
Radio toggles.
Small loading animation.
Big loading bar.
Tooltip box.
Navigation arrow buttons.
Three different size buttons (tiny, small and normal).
Icon buttons.
HTML like table.
Custom cursor.
All the elements are made to work with the GUILayout class.