Xynth Window System
Mir
Y Window System
DirectFB
Wayland
Metisse
XQuartz
xmodmap
SimpleX
Xynth Window SystemMir - The purpose of Mir is to enable the development of user interfaces shells.
Y Window System - Y Window System is a platform that allows you to improve the speed, working, and efficiency of the application in your operating system and helps you to increase the responsiveness of applications similar to any locally based app.
DirectFB - DirectFB is a web-based platform that provides you with complete access to a software library that you can use for the acceleration of graphics, handling the input devices, and others for your Linux operating systems.
Wayland - Wayland is intended as a simpler replacement for X, easier to develop and maintain.
Metisse - Metisse is an open-source software solution that is used for a seamless implementation of an interface on your desktop.
XQuartz - The XQuartz project is an open-source effort to develop a version of the X.