Luftballons seeks to be a fully featured, free software suite for cutting-edge 3D game production. At present, Luftballons consists of a deferred-rendering-oriented framework for constructing realtime rendering pipelines. It is built on top of OpenGL.
Luftballons was designed to make it easy to express any rendering pipeline. Unlike many other open source engines, Luftballons was explicitly designed to easily articulate deferred rendering pipelines, though forward rendering is certainly possible.
Luftballons was designed to expose much of the power of raw OpenGL, but to make the performance decisions for the programmer. Just tell us where the fragments go, and we'll figure out the fastest way to feed the data through the GPU.