9wm

9wm is an open source stacking window manager for X11, written by David Hogan (dhog) in 1994 to emulate the Plan 9 Second Edition window manager, 8½. Many later minimalist window managers for X were either inspired by, or directly derived from, 9wm. 9wm takes only 0.4 MB in RAM.

The README file in the 9wm source distribution describes it like so:

9wm is an X window manager which attempts to emulate

the Plan 9 window manager 8½ as far as possible within the constraints imposed by X. It provides a simple yet comfortable user interface, without garish decorations or title-bars. Or icons. And it's click-to-type.

9wm has an undocumented -nostalgia option, for a Blit cursor, which John Mackin insisted on.

Window geometry is described by "sweeping out" a rectangle on the screen. To sweep, click and hold the right button at one corner of the desired rectangle, move the mouse to the diagonally opposite corner, and release the button. Placing new windows and resizing existing windows are done by sweep operations.