Gravity Sim is a free Android game developed by Atom Mobile Applications. It lets you create your own virtual universe using slightly modified real-world physics. With its realistic model of gravity, you can throw planets around stars, moons around planets, and customize everything in your universe.

The game also features path tracing, time control, and zoom in/out functions. You can adjust the variable masses of every object and choose from 5 classes of objects with various textures. Additionally, you can lock on and follow objects in orbit, use multi-touch support, and cycle through objects you placed.

Overall, Gravity Sim provides an excellent gravity experience unparalleled on the Play Store. It has an intuitive, easy-to-use interface and offers an unlimited 2D universe to explore and create. For a more efficient and beautiful simulator, you can also check out the developer's new app, "Gravity Sim 3D".