YASRT

The name YASRT stands for Yet Another Simple RayTracer. YASRT was designed to be a stochastic raytracer. It uses the raytracing algorithm to generate realistic pictures from textual descriptions of three-dimensional scenes. By using Monte Carlo raytracing techniques, YASRT supports features such as smooth shadows, depth of field, fuzzy reflections, etc.
By using advanced raytracing techniques, YASRT can simulate realistic optical phenomena such as: reflection (objects can be reflected in mirrors), refraction (object can be seen through other transparent objects), shadows are cast when the light is blocked by one or more objects, objects have different surface properties, etc.
YASRT is a program taking one or more files (text or binary files, depending on the platform) for input and generates a picture (binary file) of the scene described in these files. A description language allows artists to describe the scene to be rendered. Alternatively, it is possible to use different tools to export scenes from different 3D authoring tools. These tools are described later in this document.
On some platforms, YASRT also supports the 3D Studio file format internally. Note that the support of the format is limited to the features present in YASRT (for example, image mapping is not yet supported in YASRT).
Raytracing is an algorithm that can be used to produce photo-realistic pictures of  three-dimensional virtual worlds on a computer. It simulates the propagation of light through an environment by tracing rays of light in a scene to determine which objects they interact with. It also models physical properties of lights, objects and the interaction between them.

NOTE:

YASRT is free for personal use.