SC StringSet - You can download and install this program on your computer, and always have a guitar tone generator available. It's easy to use; you simply select the string you want to tune, and a concert pitch tone is played on your computer.

AP Guitar Tuner - This is a guitar tuner: with this program, you can simply pluck a string in front of your computer's microphone, then the program listens to the pitch and visually shows you when your string is in tune.

Audacity - This is a digital audio editor. You can use it for multi-track recording. You can also manipulate songs; for example, you can slow down the tempo of a song without changing the pitch. To export a song as an mp3 you may be asked for this .dll file.

Fretboard Warrior - This is a simple Flash game that's designed to help students memorize the notes on the fretboard.