Downloading the CUDA toolkit DMG works, but the installer fails with a cryptic "package manifest parsing error" error after selecting packages.
Running the installer from the command line using the binary inside fails in a similar manner. The log file at /var/log/cuda_installer.log basically says the same:
Apr 28 18:16:10 CUDAMacOSXInstaller[58493] : Awoken from nib!
Apr 28 18:16:10 CUDAMacOSXInstaller[58493] : Switched to local mode.
Apr 28 18:16:24 CUDAMacOSXInstaller[58493] : Package manifest parsing error!
Apr 28 18:16:24 CUDAMacOSXInstaller[58493] : Package manifest parsing error!
Apr 28 18:16:24 CUDAMacOSXInstaller[58493] : Package manifest parsing error!
I have a prior version of cuda 7.5 installed, which (a while ago) was done through the same process without error.
(OS X 10.11, GeForce GT750M)