Star Chart - Stellarium is a planetarium software that shows exactly what you see when you look up at the stars. It's easy to use, and free. Read more about Star Chart.
SpaceX Falcon 9 Lander - Try (and fail) to land Elon Musk's SpaceX rocket
Google Sky Map - Google Sky Map is a free hand-held planetarium that allows you to identify stars, planets and more.
Astronaut - You're an astronaut. Click to watch random videos in space.
Code NASA - 253 NASA open source software projects
Universal Paperclips - Make paperclips not war