A games engine is the core of any game. It can make it run on multiple platforms like Xbox, playstation and Wii. It provides a working enviroment to to quickly and efficiently design and create games. The games with the best engines have better graphics, better sound and would probably include Havoc physics. Havoc is an middleware extension to the game engine, as is Speedtree that can be used to render a large amount of objects ingame.
Physics engines
The main purpose of a physics engine is to make life like physics involving gravity, collision detection, particles such as explosions and, in more sophisticated engines, ragdolls.
Ragdoll physics treats a characters “dead” body as a series of rigid bones connected by hinges at the joints, making it react as it would in a real life situation.
Unreal
The Unreal game engine is a significant game engine as it was the first to integrate rendering, collision detection, AI, visibility, networkng and filesystem into one complete engine. (Taken from http://en.wikipedia.org/wiki/Unreal_engine). This picture is a comparison between all three Unreal game engines.
Picture source: http://content.answers.com/main/content/wp/en/thumb/5/53/250px-Unreal_Engine_Comparison.jpg
The core of Unreal engine is written in C++ and is very portable.
Havok Physics
Havok is a middleware engine
Game Engines:
DOOM, id software
Unreal engine, Epic
