Mitsuba is a research-oriented rendering system in the style of PBRT, from
which it derives much inspiration.  It is written in portable C++, implements
unbiased as well as biased techniques, and contains heavy optimizations
targeted towards current CPU architectures.  Mitsuba is extremely modular: it
consists of a small set of core libraries and over 100 different plugins that
implement functionality ranging from materials and light sources to complete
rendering algorithms.

In comparison to other open source renderers, Mitsuba places a strong emphasis
on experimental rendering techniques, such as path-based formulations of
Metropolis Light Transport and volumetric modeling approaches.  Thus, it may
be of genuine interest to those who would like to experiment with such
techniques that haven't yet found their way into mainstream renderers, and it
also provides a solid foundation for research in this domain.

Mitsuba comes with a command-line interface as well as a graphical frontend to
interactively explore scenes.  While navigating, a rough preview is shown that
becomes increasingly accurate as soon as all movements are stopped.  Once a
viewpoint has been chosen, a wide range of rendering techniques can be used to
generate images, and their parameters can be tuned from within the program.

WWW: http://mitsuba-renderer.org/