Simplestroke is a simple utility that detects mouse gestures.  It
currently detects sixteen pre-defined mouse gestures and prints the
name of the detected gesture to stdout, if any.  The output can then
e.g. be used in a simple shell script to execute commands.

Example usages could include closing windows in i3 by drawing a Z over
them or other window manipulations, or pausing your music player by
drawing a left-to-right line.

WWW: https://github.com/t6/simplestroke