Here is the first release of CastingStage, that was first previewed here. It is a simple raytracing engine made using Cocoa. It intends to be lean and mean, easy to use, and to showcase several Mac OS X technologies, such as bindings, CoreData, Grand Central Dispatch, and so on.
Here are the currently supported features :
You can view some screenshots or download the application (requires Mac OS 10.6 for now, Leopard support coming soon). And the code is under the MIT license — so feel free to play with it !