Easystroke is a gesture-recognition application for X11. Gestures or
strokes are movements that you make with your mouse (or your pen,
finger etc.) while holding down a specific mouse button. Easystroke
will execute certain actions if it recognizes the stroke; currently
easystroke can emulate key presses, execute shell commands, hold down
modifiers and emulate a scroll wheel. The program was designed with
Tablet PCs in mind and can be used effectively even without access to
a keyboard.

WWW: http://easystroke.sourceforge.net/