MouSing

Create music by sliding your finger around on the screen, making sounds similar to a musical instrument known as the Theremin. One axis of movement alters pitch, and the other controls volume, with a highly intuitive interface that enables the user to play melodies by ear. Optional controls display pitch, frequency, and notes on a keyboard, and the pitch range may be defined.

No ads, free, fully functional. Voluntary contribution suggested via in-app billing, with no nags.

A desktop Windows version is also available on the creator's website. MouSing follows in the tradition of continuous-pitch musical instruments such as the theremin, Tannerin, and ondes Martenot.