Steam's new Remote Play Together feature had its official launch last week, and it's the perfect way to enjoy Catastronauts with friends who are further afield!
The feature allows friends to play local multiplayer games online together. Only the host will need to have the game in their Steam Library, and there's no need to install or set up additional software - you just need the game and the Steam client and you're good to go!
To use Remote Play Together with Catastronauts, just launch the game as normal. Then open the Steam Overlay with SHIFT+TAB, right click on a friend in the friends list, and select Remote Play Together. Make sure you both have your controllers plugged in ready to go before starting!