Unreal Engine is a complete game development framework for PCs, Xbox 360, iOS, and PlayStation 3, providing a vast array of core technologies, content creation tools, and support infrastructure content.
Every aspect of the Unreal Engine game development toolset has been designed with ease of content creation and programming in mind, with the goal of putting as much power as possible in the hands of artists and designers to develop assets in a visual environment with minimal programmer assistance, as well as giving programmers a highly modular, scalable and extensible framework for building, testing, and shipping games in a wide range of genres.
Website & download: http://www.unrealengine.com
Unity is a game development ecosystem: a powerful rendering engine fully integrated with a complete set of intuitive tools and rapid workflows to create interactive 3D content; easy multiplatform publishing; thousands of quality, ready-made assets in the Asset Store and a knowledge-sharing Community.
Website & download: http://unity3d.com
Panda3D is a game engine, a framework for 3D rendering and game development for Python and C++ programs. Panda3D is Open Source and free for any purpose, including commercial ventures.
Website & download: http://www.panda3d.org
The Doomsday Engine allows you to play the classic first-person shooters DOOM, Heretic, and Hexen using modern technology, with hardware accelerated 3D graphics, surround sound and much more.
Download : http://sourceforge.net
Arianne is a multiplayer online engine to develop turn based and real time games, providing a simple way of creating the game server rules and clients like our MORPG Stendhal. Our engine Marauroa uses Java and SQL for hosting hundreds of players on a solo host.
Stendhal is a fun friendly and free multiplayer online adventure game with a huge and rich world. With hundreds of NPCs and different quests, features like the Travel log and achievement system keep track of progress. Thousands of creatures are ready to fight, above and below ground, and as players level up they can compare themselves on a detailed stats website.
The engine Marauroa provides a simple way of creating games on a portable and robust server architecture. Marauroa manages the client server communication and provides an object orientated view of the world for game developers. It handles database access in a transparent way to store player accounts, character progress and the state of the world.