The RealTime Tuner is a freeware Macintosh program for musicians who are interested in alternative tunings, or who might become interested in them if they had a convenient way of experimenting with them. The use of tunings other than standard Equal Temperament adds a fascinating extra dimension to the musical experience.

The program makes it possible to play a MIDI instrument in any twelve-tone temperament. It also provides ways of shifting the temperament to center on a different tonic key, and to do this instantly as the music progresses. This means that Just Intonation, well-tempered tunings, and other historic and ethnic temperaments can be made to follow the harmonies of the music instead of constraining them. Artists need no longer restrict themselves to Equal Temperament simply because some of the chords they wish to play are distant from those of the starting key.

By touching a key in a silent `tuning octave' the player can immediately reset the current tonic relative to which the other degrees of the scale are to be tempered. For simple music the retuning can be carried out automatically by the computer. A special escape key allows a retreat to Equal Temperament when expedient. Preset tunings can be actuated from a pedal. Tuned performances can be recorded and edited as MIDI files. These and other capabilities make it practical to use alternative tunings in today's musical environment.