A raytracer trying to aid lighting designers and architects by predicting the light levels and appearance of a space prior to construction. It uses a hybrid approach of Monte Carlo and deterministic ray tracing. Available for Unix.

A GUI the YAFRAY raytracer written in Python. Downloads, screenshots, and FAQ. Available for Linux and Windows.

An object oriented library with API in C++ and Python for synthetic rendering, which provides a common environment and description language to treat light distribution in three dimensional spaces. Available for Linux and Windows.

Ray tracing library written in c++ with python bindings. Source code, documentation, galleries, tutorials available. Binaries for Windows, seems to be portable to Unix platforms.

Plug-in for Rhino, uses both raytracing and radiosity to create single-frame images and animations. Product description, gallery, training, evaluation download, and purchasing. For Windows.

Regular awards for best raytraced still images and animations submitted by the public. Recent winners, voting on the current round, and the topic and rules for submitting to the next round.

An overview non technical article on ray tracing also covering some history of the subject.

A ray tracer distributed as C source, supporting almost every Unix version, Windows NT and Mac OSX.

Lots of information on ray tracing. Updated once or twice a year.

Test bed system for physically based photo-realistic image synthesis, mostly radiosity based. Unix based.