List of Useful and Interesting Open-source Softwares and Websites
FlightGear
A highly physics-accurate flight simulator
Stellarium
A realistic and accurate planetarium software
Ray Optics Simulation
Interactive and rich ray optics simulator
Math & Physics Applets
Treasure trove of simulators by Paul Falstad
Engine Simulator
Real-time IC engine simulation by AngeTheGreat
Map of The Universe
A quarter-map of our observable universe to scale based on data collected by SDSS
NASA Eyes
Real-time data of Earth, Solar System, Asteroids & Exoplanets
Celestia
Open source 3D visualization of space in real-time