Fluxbox - Fluxbox is a window manager for X that was based on the Blackbox 0.61.1 code.
Wayland - Wayland is intended as a simpler replacement for X, easier to develop and maintain.
IceWM - icewm home page . Bug Tracking. If you have a patch, a bug report or a feature request to submit, please do so at the icewm project page at SourceForge.
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.
qtile - Qtile is a full-featured, hackable tiling window manager written in Python.
XQuartz - The XQuartz project is an open-source effort to develop a version of the X.