Thomas Dinges is working on a standalone version of the Cycles renderer. The current version is still very simple, but it paves the way for integration of Cycles in to other 3D apps.
Thomas Dinges writes:
Cycles is nicely integrated into Blender, but can also be build as a standalone renderer. 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).