This is by far the best guitar scale reference for practice and teaching in the App Store.
You can view and print scales in any key and in any mode. You can also view and print a number of other scale-like forms (pentatonic, bebop dominate, etc.). The fretboard, in standard tuning, can even be viewed and printed out in CAGED boxes.
You can even plug in a chord and see a fretboard of arpeggios which you can print out.
Its insanely great!
But I still want more:
More, or user-created, scales. Arbitrary user-created tunings. Arbitrary number of strings so it can handle mandolin and bass, etc.
Still, nothing else out there is even close.
Play guitar? You need this.