Rex Engine is a 2D platformer engine for Unity! It gives you a custom physics engine tailor-made for building tight, crunchy 2D games. Additionally, it gives you a huge library of classic sidescroller mechanics like running, jumping, attacking, swimming, dashing, and more! This video shows what's new in version 1.02, including charge shots, the ability to run while a button is held, breakable blocks, and damage numbers!
You can purchase Rex Engine here: http://u3d.as/RLr
Rex Engine official site: http://www.skytyrannosaur.com