Prota OS is free and can be downloaded here if you want to install it on your Raspberry Pi.
We are supporting a free Raspberry Pi version as we believe that the community of makers has the capacity and passion to shape what's going to be the next big thing in the IoT universe.
This OS will, therefore, remain free. We will in the near future and the possibility for a small subscription to get additional features and apps, leaving, of course, the choice to keep the free version only.
You can use Prota OS on as many devices as you want.
Go to the downloads page and click the "Download" button. We created a single Prota OS image that works multiple* versions of Raspberry Pi, including Raspberry Pi 3.
*Prota OS is compatible with Rpi B, B+, 2, 3. Please note that currently Prota OS is not compatible with Raspberry Pi 0.