Wayland - Wayland is intended as a simpler replacement for X, easier to develop and maintain.
XQuartz - The XQuartz project is an open-source effort to develop a version of the X.
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.
i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.
qtile - Qtile is a full-featured, hackable tiling window manager written in Python.
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.