xstroke is a full-screen gesture recognition program written for the X Window System. It captures gestures that are performed with a pointer device, (such as a mouse, a stylus, or a pen/tablet), recognizes the gestures and performs actions based on the gestures. xstroke has been developed on Linux systems, (i386 and StrongARM), but should be quite portable to any UNIX-like system with X.
Xscribble is an X application that allows a user of a touch screen to input characters into X applications, using a uni-stroke (Graffiti like) alphabet. It uses the X test extension to allow synthesis of characters as though they had been typed on a keyboard. Though it was designed for Linux on PDAs it might work with Tablet PCs as well.
Yudit is a Unicode text editor for the X Window System. It can do True Type font rendering, printing, transliterated keyboard input, and handwriting recognition with no dependencies on external engines. Its conversion utilities can convert text between various encodings. Keyboard input maps can also act like text converters.