gStrings is a chromatic tuner application measuring sound pitch and intensity.

It will let you tune any musical instrument (violin viola violoncello bass guitar piano wind instruments your own voice/singing).

Features include:
1. multiple built-in instruments and tunings
2. support for user-defined custom tunings
3. a long list of built-in temperaments (just pythagorean meantone comma etc.)
4. support for user-defined custom temperaments
5. orchestra tuning (shifting/redefining tone frequencies)
6. pitch pipe
and many more.

If you were looking for a guitar tuner try it!

Thank you note: most of the historic temperaments were included courtesy of NetCat AG.