1)   Guitar-Online Tuner 2.1.0.3
This guitar, mandolin, ukulele, fiddle, banjo, bass guitar tuner allows standard and open tunings.

 2)   Chord Alchemy 4.0
ChordAlchemy is the ultimate tool for chord lookups, reverse chord lookups and hearing how they sound. ChordAlchemy supports 100+ tunings, Added Bass, No Root, Scales, Chord Pages and Printing. Superb user interface for easy chord generation control!

 3)   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.

 4)   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.