Simulator - Ray Optics Simulation
A very cool optics simulator.
Iceberger
How would that iceberg really float? Lots of illustrations that show "the $FOO iceberg" show a berg floating in an orientation that's very unlikely. This site lets you draw the vague outline and see how it might really end up.
Lunar Flight - Basic Flight Tutorial - YouTube
Really useful basic tutorial for flying Lunar Flight in VR.