Cycles is nicely integrated into Blender, but can also be built as a standalone renderer, which Blender developer Thomas Dinges is currently working on. The standalone application can be used for testing purposes but also allows an integration into other 3D programs. The code is still experimental and the application is quite simplistic, but it can already be used and also works with features such as OSL or GPU rendering (if compiled with those features). Check out some screenshots from the initial builds so far...
I'd like to give you an update on the Cycles standalone renderer.
I worked on the code the past few days, it's easier to build now and the XML API has been updated a bit as well.
Please get in touch with us, if you like to help out, and want to integrate Cycles into other 3D programs for example.
I'd also like got get feedback on an improved API, I don't think XML is the best thing here.