easystroke is a gesture-recognition application for X11. It aims to be highly configurable while at the same time providing an intuitive user interface. It was designed primarily for use on a Tablet PC, but it also works well with a mouse.
High Sign is an application that allows users to easily create and map custom gestures to perform common actions on their Windows PC. Unlike some other mouse gesture recognition software, the user is not limited to a set of predefined gestures. Written in C#, allows plugins.