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).
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.