Arguably the best free Flash game ever created. The game is a platformer by genre, with a few puzzle elements that come from the stunts you must pull involving jumps. N stands for Ninja, as you play a small stick figure ninja who is capable of running at very high speed, wall jumping, and jumping very long distances. The game has staying power due to the users' ability to make their own maps as well as play the levels other people create, though it could be months before you get through all the normal game's levels.
You must avoid a variety of enemies, all of which kill you brutally and violently (though it couldn't be called disturbing, he's only a stick figure) which is made extra entertaining due to the game's physics engine.
I almost got fired because I got caught playing N at work again. Dammit too, because I was *this* close to finally beating Episode 49!