Click a note to play. Hold CTRL to hold.
Displays notes generated by 3x (horizontal) and 5x (vertical) frequency bases, with note names and errors in cents wrt equal temperament (12-EDO). Octaves ignored.
On playing a note, notes with the same name are emphasised, and notes within 50 cents of the same pitch are highlighted in a different colour.

Even-tempered: - off for perfect Pythagorean pitch, on for equal temperament (12-EDO)

Read more on github and my blog.