Y Window System
The Y Window System (Also known as Y-Windows) is a windowing system, consisting of a window server and a client library for writing applications. It was written by Mark Thomas as the subject of his Master thesis at Imperial College, London. It is intended to be a successor to the X Window System, hence the name. It differs from the X Window System in having an integrated widget set and ground-up support for things like an alpha channel, which allows transparent or translucent windows.
At the end of his Master Thesis he had a working system with some applications. Later he released the code and set up a community project. Y uses SDL, and in theory can run under any system that supports SDL.
As of 2005, the project is incomplete and not undergoing active development; the developers do not have time to work on this project. [1]