SimPhy - Interactive 2D & 3D Physics simulation software
Terraria - Dig, Fight, Build! The very world is at your fingertips as you fight for survival, fortune, and glory.
Physion - Physics Simulation Sandbox
Roblox - Reimagining the way people come together.
Open Source Physics - Open Source Physics is an open-source Java software project for teaching and studying physics.
Step - Step is an open-source two-dimensional physics simulation engine (KDE).