Physion is described as 'Physics simulation software for creating interactive physics simulations and educational experiments'. There are three games similar to Physion for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and Armor Games. The best alternative is Mutilate-a-Doll 2. It's not free, so if you're looking for a free alternative, you could try SimPhy or FisicaLab.
Simphy is a simulation software to create 2D and 3D simulations with easy drag and drop options. You can create different types of bodies inside its physics world with different parameters like restitution, friction, velocity etc.
FisicaLab (can be pronounced as PhysicsLab) is an educational application to solve physics problems. Its main objective is let the user to focus in physics concepts, leaving aside the mathematical details (FisicaLab take care of them).