FlashPunk is a free ActionScript 3 library designed for developing 2D Flash games. It provides you with a fast, clean framework to prototype and develop your games in. This means that most of the dirty work (timestep, animation, input, and collision to name a few) is already coded for you and ready to go, giving you more time and energy to concentrate on the design and testing of your game. For more information, check out FlashPunk.net.
Here are games on NG that were made with FlashPunk!