Beautiful simulator! I'm a big fan of gravity and fluid simulators and this is the nicest looking one I've seen! It looks great and runs smooth! I see that you are responding to reviews and looking for suggestions as well, so I've come up with a few: -Add a bit of customization, allow the user to change the mass, shape, and maybe even color of each object. -Allow interaction with the objects, let the user apply a force, spin, and trajectory during the creation of the object as well as after creation. -the Rock Tumbler is a bit bare bones, I expected the rocks to become more faceted as they rolled around. -Let the user mute the music and/or sound effects if desired -I don't know if it would be possible but I don't think I've ever seen a 3D fluid simulator toy. It might be a bit computationally heavy, but I know in programs like Maya the process can be simulated with spheres. Maybe look into that! That last one is obviously a big challenge and I don't expect you to go crazy if people are only paying a dollar. Thank you for creating a beautiful app for me to play with!