Ominator is an iOS app that generates music along to your humming, responding to the pitch you hum.
The timbre is rich and relaxing, with hints at accompanying melodies. As you hum louder, you can hear higher harmonics in the note that you are singing, and the music continues even when you pause to take a breath, which invokes the feeling that you are able to hum continuously without stopping.
This video capture is a poor representation, as you cannot hear the humming. When used with headphones, your voice blends with the sounds in your head to create a truly encompassing musical experience.