Digital Guitar Tuner is a free Windows software, which let's you accurately tune your guitar using direct input, microphone or MIDI tones. Now a new version 2.3 is available for downloading. Now it features 27 tuning types!

Features:

* High accuracy (uses 16 bit / 44100 Hz input!)
* You can tune guitars with no signal output (through microphone)
* 27 different tuning types (standard, lowered, dropped, open tunings, Hawaiian etc.)
* Modulation of root frequency
* Tuning with midi tones
* Nice and simple environment
* it's free!