Unreal Engine 3 is a complete game development framework for next-generation consoles and DirectX9-equipped PCs, providing the vast array of core technologies, content creation tools, and support infrastructure required by top game developers.
Unreal Editor makes it Happen. This WYSIWYG tool allows for content creation at lightning speed. The editor itself is actually a suite of tools designed for realizing your content as quickly and easily as possible. For example, you can test gameplay in one window while you edit content in another.