aewm

Decklin Foster wrote aewm in the late 1990s with 9wm as the model. It does what is necessary and nothing more: a title bar with a close box, moving and resizing with the mouse, click to focus, no configuration file and no virtual desktops. Menus and launchers were pushed out into separate small programs that talked to the window manager through X properties, so the core could stay minimal. The code is commented like a textbook, and that was the intent: it should be understandable in an evening.

That is exactly why it became a starting point for others. evilwm began as aewm with the decorations removed, and the C++ rewrite aewm++ led on to pekwm. Anyone who wants to know what a window manager actually does, beneath the wallpaper and the animations, still reads aewm before anything else.