1)   Guitar and Bass Ear Trainer 1.5
Play-along ear-training course for guitar, bass, and other fretboard instrument players. Learn to play effortlessly by ear. Develop the ability of playing whatever is in your mind without hesitation and without mistakes, improve your improvisation.

 2)   Absolute Fretboard Trainer 3.x
If you want to master the fretboard of guitar, bass, banjo, mandolin, or other fretboard instruments, the Absolute Fretboard Trainer will take you there. Step-by-step exercises will help you develop instant knowledge of each and every note.

 3)   Guitar Power - PalmOS Edition 1.1.0
The Ultimate Scale, Chord and Arpeggio Reference for Guitarists. Guitar Power is an interactive learning system. Quickly and easily use scales, chords and arpeggios. Any style or level - learn the secrets of the pros and play like your guitar heroes.