The dywapitchtrack library computes the pitch of an audio stream in realtime. The pitch is the main frequency of the waveform (the "note" being played or sung). It is expressed as a float in Hz. dywapitchtrack is based on a custom-tailored algorithm which is of very high quality, very accurate (precision < 0.05 semitones), with very low latency (< 23 ms) and very low error rates. It has been thoroughly tested on the human voice.
ZebraTuner is a guitar tuner and generic instrument tuner. It compares frequencies detected in the signal coming from the microphone to standard or user-defined notes, displaying the results in both graphical and textual form. The number of notes tested and their frequency is configurable, so it can be used for other instruments and other tunings besides those based on equal temperament (e.g. just intonation-based tunings).