AI Duet is a Google AI experiment.

From the site: AI Duet lets you play a duet with the computer. Just play some notes, and the computer will respond to your melody. You don’t even have to know how to play piano—it’s fun to just press some keys and listen to what comes back. You can click the keyboard, use your computer keys, or even plug in a MIDI keyboard. It’s just one example of how machine learning can inspire people to be creative in new ways.