From Audacity Wiki
|This is a small collection of tips about instrument tuning tasks for which it could sometimes be useful to use software other than Audacity (even though you might use Audacity for most of your audio creation and editing).
You can easily tune an instrument with a computer, a sound input such as microphone or line-in and the following software:
- GTune - Windows
Free VST Tuner.
- Digital Guitar Tuner - Windows
Free, 27 tuning types.
- FREE Guitar Tuner - Mac OS X
- various shareware regular and strobe tuners - Mac OS X
- GuiTuner - Linux
Free, guitar tuner for Linux.
- KGuitune - Linux
Free tuner for guitar and other instruments.
There are many online guides to guitar tuning, for example this one.