X Window System
@ https://en.wikipedia.org/wiki/X_Window_System
Wikipedia entry for the x window system, used by many Unix-like systems.
dynamic window manager (dwm) by suckless
@ https://dwm.suckless.org/
A lightweight, fast (by their own accounts), window manager.
spectrwm
@ https://github.com/conformal/spectrwm
Another window manager that is meant to expand on the ideas of dwm further possibly making it better to use.