Notice: This page is still being incubated.
Render Cache is a Java(!) example of interactive ray tracing. It renders only a subset of all pixels and uses an intelligent caching mechanism to predict the rest.
"State-of-the-Art in Interactive Raytracing", Wald & Slusallek, pdf
VirtualRay Engine with a shareware game available.
OpenRT. Attempt to build a OpenGL like real time toolkit. Commercial, but with noncommercial tryouts (at the time only for linux). Impossible to find a working demo build with OpenRT.
Ono-Sendei RT raytracer Actually working raytracer with source. Very Nice.