Unity Game Engine
Unity makes it easy for developer to develop and publish games for multiple platforms across desktops, gaming consoles and mobile devices. Unity’s intuitive, extensible Editor workspace allows you to rapidly assemble your scenes. There are tons of assets (free and paid) available in the Unity asset store that you can import and use in your project. Mecanim, a powerful animation system that lets you animate just about anything is deeply integrated in the Unity engine.
Unity has two versions, the free version of Unity and Unity Pro. Difference between these two versions can be viewed here.
Below are some games that were developed with Unity.