Algodoo

Now that Phun can do proper rings, doesn't have sticking issues with large polygons, and the springs are un-fuxored, I've finally been able to build my ringworld offroad obstacle course! Look ma, no gravity!
After the ring has spun up to speed, the door will disappear and you can attempt to traverse the inner circumference of the ring. Watch out for Coriolis forces! At some points, the dynamics of spin-generated artificial gravity can help you, but in others they can be a pain in the butt. Also take note of the wind. You'll be fighting it every inch of the way.

DIZZINESS WARNING! It's a very large ring and doesn't need to spin very fast, but you may want to zoom out a bit and/or turn on rotational tracking because it can still be disorienting.

My lobster can do it! Can you? Arrow keys to move, UP to bend at the body hinge to help get over complicated obstacles.
Also, LOL textures.

Edit: Oh wow, didn't know people would like it so much! Thanks! The lobster's an old project, though.