Which features are not supported when GPU rendering? This question would seem to have a straightforward answer, but after reading through the Blender Manual's section about GPU Rendering, and also searching elsewhere online, I have not been able to find a list of which features are not supported when rendering with a GPU.

I remember that Open Shading Language is not supported, but I'm sure there are other unsupported features that I either don't know about or have forgotten about.

Does anyone know if there is a resource page available somewhere where I can get a list that makes this clear? Thanks.
Unless I misunderstand what you are looking for, the Blender manual seems to have a pretty thorough list of supported features per device.

As of current Blender 2.78, this list includes all supported computing hardware types, like CPU, GPU, OpenCL, or CUDA; and the available , experimental, and unsupported features for each of them, like motion blur, hair, volume, smoke/fire, subsurface scattering (SSS), Open Shading Language (OSL), CMJ Sampling, Branched Path integrator, and displacement subdivision.