FMIT is a graphical utility for tuning your musical instruments, with error and volume history and advanced features.

Features:

• Estimation of the fundamental frequency (f0) of an audio signal, in real-time.
  (the f0, not the perceived pitch)
• Harmonics’ amplitude
• Waveform’s period
• Discrete Fourier Transform (DFT)
• Microtonal tuning (supports scala file format)
• Statistics
• All views are optional so that the interface can be as simple as possible.
  (make it easy to see on a distant screen)
• Can support OSS, ALSA, PortAudio and Jack sound systems.
• Everything runs under Linux, Mac OSX  and Windows 

gillesdegottex.github.io/fmit