GNUitar is guitar effects software that allows you to use your PC as guitar processor. It includes the following effects: wah-wah, sustain, distortion, reverberator, echo, delay, tremolo, vibrato, and chorus/flanger.

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Source:  http://sourceforge.net/projects/gnuitar

Generate great-looking guitar chord sheets

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Source: http://sourceforge.net/projects/chordsheet 

FretBoard is a PalmOS reference tool for stringed instruments like Guitar, Bass, Banjo and many others. It displays notes, chords and scales on any instrument.

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Source: http://sourceforge.net/projects/fretboard