This was the theme I disliked most, after dust bunnies. Oh well. Some ideas I had so far:

• An adventure game where the hero is on a quest to figure out the metaphorical length of a piece of string.
• A puzzle game, where in each level you have to resolve a space-time singularity by adjusting the length of closed strings in order to localize tachyons around it. (See wikipedia entry on string theory.)
• Platformer where you play a ball of wool made of many pieces of string.
• Some more which all require the use of box2d or chipmunk which I want to avoid.

Physics are rather broken, and I didn't have time to add any of the features I had planned, but at least I did manage to upload something playable. Given that I didn't have a lot of time during the week and it was my least favorite theme, I guess that already is a bit of achievement :)

Because I forgot to add any readme, the idea is this:

You control a small airship with a piece of string attached, flying around in a small hadron collider. The floor is electrically charged. Only when the length of the piece of string is enough to touch the electric ground, your ship has power.

Also, some tachyons escaped during an experiment, and you have to neutralize them to prevent a black hole from forming. You do that by shooting them with water. If the tachyons form a black hole (time runs out), you fall off the airship or get sucked into the eternal space-time void, or if a tachyon vaporizes you... you die. If you can shoot all the tachyons in time however... you advance to the next level.

Made one here.