The current model of the HDHomeRun Prime accepts CableCARD and then broadcasts that signal over your local network. It's the same as the regular HDHomeRun devices do for OTA TV, but it's naturally not free television.
You get three tuners on the current model which means three different streams can be played or recorded at once on different devices on your network. You can stack them but it means paying for another Prime and another CableCARD. But later this year, the Prime is getting a redesign and six tuners. So it's twice as good!
The new box is smaller than the existing model so it'll take up less space in your setup, but the extra tuners mean you'll be able to play six different streams across your network at the same time. So if you've a large family, everyone can watch something different and you'll only need one box and one CableCARD.
There's not a whole lot more to say about it right now, and pricing and exact availability is still to come. It's also worth reminding that this product is only available in the U.S. Nevertheless, if you're a current Prime owner or have been thinking about getting one, this is a piece of good news for your home entertainment.