http://www.verlocityengine.com/
Open-source Flash engine designed to be easy, yet powerful. Free for commerical and personal games
Verlocity is an incredibly easy-to-use, yet extremely powerful pure Actionscript 3 Flash engine primed for game development. Built-in components for entity management, real-time sound analyzation, location-based sound objects, states with transitions, achievements, impressive debugging tools (console and concommands), localization, camera, inventory, saving/loading, soundscapes and a whole lot more. Completely expandable and built around making game development easy and enjoyable.