INDIGO RENDERER

Indigo is a gratis, actively developed render engine. Indigo uses methods such as Metropolis Light Transport, Spectral light calculus, and virtual camera model. Indigo is capable of highly realistic renders. Scene data is stored in XML format.
Indigo features Monte-Carlo path tracing, experimental support for Bidirectional path tracing and MLT on top of bidirectional path tracing, distributed render capabilities, and progressive rendering (image gradually becomes less noisy as rendering progresses). Since Version 0.7 test 5 it also supports SSS and has its own Image Format (.igs). A Post-render tone mapping tool is in development under the name Violet, this is open sourced under GPL.
Indigo can be used by a diverse collection of modeling programs, such as Blender, 3Ds Max or Maya for which suitable exporters are available.
Currently Indigo is only developed for the Microsoft Windows operating system, although it can be run very well through WINE in Unix-like environments (i.e. Linux), and can be used in emulated mode in MacOS (this is very slow, however).