Space Engine - Space Engine is a realistic virtual Universe you can explore on your computer.
Celestia - Real-time 3D visualization of space
OpenSpace - OpenSpace is open source interactive data visualization software designed to visualize the entire known universe and portray our ongoing efforts to investigate the cosmos.
Stellarium - Stellarium is a free open source planetarium for your computer.
Gravity WebGL - A gravity simulator, with updated movement controls
Universe Sandbox - Universe Sandbox ² is a physics-based space simulator where you can simulate Events and even break physics and friction with certain features.