9wm is a stacking window manager GUI made for the X Window System. The 9wm window manager is an open-source program, and is written in C with no dependencies. 9wm was made to work with Plan 9, a free operating systems from Bell Labs, and is based on a prior version of a GUI called 8½ .
Techopedia explains 9wm
One unique feature of 9wm is a lack of common keyboard operations. For example, the program contains windows resizing commands done by "sweeping," a mouse operation that visually defines the window size. This and other mouse-based operations enable various tasks in 9wm.
Another characteristic of 9wm is its relative simplicity. This adds to its appeal as a versatile program for a wider range of devices and operating systems. A readme file providing documentation for 9wm specifies that it was not developed as a a customizable, sophisticated GUI, but is designed to be small and agile.