As pointed out in the excellent Real-Time Rendering blog, Sony Pictures Imageworks has released the documentation and source code for their Open Shading Language compiler. It's a slightly different take on shading languages than GLSL / HLSL / Cg. The idea is that instead of generating final colors, as in other SLs, shaders compute information about how a surface / light / whatever interacts. These shaders are then connected into a network, and complex global illumination is then calculated by evaluating the network. At least, that's my understanding from readin the introduction for five minutes.

Pretty cool stuff.