Metaphor is a component-based game engine. Rather than reinvent the wheel, Metaphor is easily designed to integrate existing libraries and middleware - whether they be open source or commercial.
Metaphor is markedly different from most game engines. Metaphor embraces aggregation (using components), thus avoiding the complicated inheritance trees that show up in many games today. An API is provided that allows registration and retrieval of your own C++ component types in a completely typesafe manner. In addition, components can be implemented in Lua allowing very rapid development and prototyping of new functionality.