Unfortunately, the Virtual Gateway is not available on Mac OS yet. It is, however, available for Linux.
If you log into app.cloud.windriver.com from Linux you will be presented with a blue Download button. This will download a zip file with a configuration specific to your device. There will be a shell script named <device name>-virtual-gateway.sh.
You may run this from a terminal to start the Virtual Gateway: ./mydevice-virtual-gateway.sh
It will prompt you for the serial port you wish to use to connect to your device. In most cases this will be /dev/ttyS0
Note: On some Linux distributions you may need to ensure that you are root or that your user is a member of the "dialout" group in order to have permissions to access the serial port.
If you have any difficulties getting this going, I'd be happy to walk you through it.
I managed to get it worked under Max OS X El Capitan without the need of any adaption in the packages and scripts.
So far what I did:
Make sure the the USB to Serial adapter is known on your Mac
If no serial are listed you might install the corresponding driver (Prolific which work for FTDI chips as well)
Once the device is listed
Open a Terminal and cd to the directory containing the package
Start the script: ./mydevice-virtual-gateway.sh
Enter the serial port as /dev/cu.usbserial-FTGACK7K for example (this is the name of the interface on my Mac)
Then enjoy the cloud...