Unity is the ultimate game development platform. Use Unity to build high-quality 3D and 2D games, deploy them across mobile, desktop, VR/AR, consoles or the Web, and connect with loyal and enthusiastic players and customers.
Cocos2d-x is an open-source and cross platform open source free 2D game engine for mobile game development known for its speed, stability, and easy of use
Starling is pure ActionScript 3 and recreates Flash's display list architecture on the GPU providing a performance unlike anything else! Starling runs in the browser and on all major mobile platforms, like iOS and Android.
VERGE 3 is an easy 2D game engine, which lets game makers create rapidly developed games in Lua and/or a custom scripting language. Verge games are immediately portable to many platforms, including (but not limited to) Mac, PC, Linux, PSP, Wii, and Xbox3