Stringed

Absolute Fretboard Trainer
Play-along course for mastering the fretboard of guitar, bass, mandolin.
http://www.absolutefretboard.com/?a=pad

ChordWizard
[Win] For guitar, banjo, mandolin, bass, ukulele, bouzouki, and others. Also offers free music theory tutorial.
http://www.chordwizard.com/

Desktop Music
Software for guitar, bass, and banjo players.
http://www.desktopmusic.com/

Funkyseagull.com
[Win - Mac] CD-ROMs for banjo, fiddle and guitar.
http://www.funkyseagull.com/

In-Tune Multi-Instrument Tuner
For tuning guitar, bass, banjo, mandolin, violin, viola, and cello. Other instruments via the pitch selector.
http://www.musicmasterworks.com/tuner.html

ScaleTool
Scale generator for guitar and piano.
http://www.scaletool.com/

Twofold Media
[Win] Description of Violin Magic Made Easy, a CD-Rom for the beginner violinist and support crew.
http://www.twofold.com.au/

Virtual Fretboard
Guitar, tenor guitar, bass, and mandolin fretboards showing chords and scales.
http://www.virtual-fretboard.com