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.