Microwindows is a windowing system which is full featured enough to be used on a PC or a PDA. The Nano-X Window System is an Open Source project aimed at bringing the features of modern graphical windowing environments to smaller devices and platforms. The project was renamed to Nano-X Window System, due to legal threats from Microsoft regarding the Windows trademark.
Read more about Microwindows: Overview, Microwindows API, Window Creation and Destruction