Trope is a generative music app for iPhone created by Brian Eno and Peter Chilvers.
Brian Eno and Peter Chilvers developed "Bloom" together, and "Trope" is very similar to it. It's the same setup, where you tap your finger in different areas of the screen to create sounds that then loop and change over time. Trope uses more drones and pads than Bloom, however, so the music you'll get it quite different and, as the developers say, darker than Bloom.
The visuals have also gotten a big bump up, offering much more variation in patterns and colors than Bloom.
Her's a short clip of Trope in action.