CraftStudio is the cooperative game-making platform. It lets you build 3D games from scratch in real-time over the Internet. Come jam with your team or join others to make your dream games come true!
This engine is very easy to use and has a pleasantly simple feel to it - while being very powerful. It is still in beta and features are being added all the time, but it is one of the best engines out there, especially at it's low price. I would thoroughly recommend it to anyone wanting to get started with game development.