Software for Your Musical Instruments?

kko asks: "After looking for tuning software for my newly-acquired violin, I stumbled upon Tutor, which is an nifty violin tuner that also helps in developing your intonation and quick reading skills. What software have you used to aid your instrument practice, and how has it helped (or hindered) you? If you are an instructor, what do you think of instrument software in your student's learning process?"