Guitar Toolkit is an iPhone app that I am finding really handy. It provides a number of guitar tools:
- fretboard reference with scales marked (below is pentatonic C major). The notes on the fretboard can be played although as an instrument it doesn't compare to a guitar.
- chord reference. Can strum the strings to hear the chord. Changing chord is too laborious for this to be useful for developing chord progressions. No tools to help with that.
- metronome for people with no innate rhythm
- tuner. This is cool, listens to the note you play and tells you what it is and how far out of key it is. I find this easier to use than the tuner in the line6 pocket pod although I use the pod's tuner if it is plugged in


