In a rather amazing blast from the past, we have this application from 2006 called Pocket Sands, which appears to make brilliant use of the 1 Ghz processor in the HTC HD2.
The software allows one to play with particle effects on screen, drawing various shapes with sand, fire, water and vegetation, and allows these various elements to interact.
The only fault with the software is the tiny icons, clearly designed more the a stylus than a finger,and the lack of accelerometer response, but the software works flawlessly nevertheless.
The cab has been somewhat difficult to find, but I have found a working download here.
Video via Apostlecreed10.