Just Intonation is a free experimental software that allows you to hear and play music in just intonation, independent of scale. You can hear in-built examples, play Midi files, or even connect a Midi keyboard and play by yourself. The application instantly optimizes the pitches for maximal consonance. In order to be as realistic as possible, the application comes with samples of real instruments, including piano, organ, and harpsichord. This allows you to get an impression how just intonation would sound like. Our vision is to demonstrate that future keyboard instruments are no longer bound to the equal temperament, rather there is a huge creative free space for the development of more consonant dynamical tuning schemes.