Guitar Trainer is an application for mobile devices that helps musicians learn the fretboard of their stringed instrument thoroughly. It supports guitar, bass, banjo, ukulele, mandolin, and cavaquinho (in standard and alternate tunings). It includes a training mode, a game mode, and a tuner. It should work on any Java device supporting CLDC 1.1/MIDP 2.0.

http://freshmeat.net/projects/guitartrainer/