Photon Engine - Independent networking engine and multiplayer platform.
Unity - The multiplatform game creation tools for everyone.
Unity Multiplayer - Create real-time, networked games.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
SmartFoxServer - Massive multiplayer platform
Blender - Blender is the open source, cross platform suite of tools for 3D creation.