Lumberyard is Amazon's own game engine for building 2D and 3D games. Its connection to the powerful Amazon network makes it easier to add multiplayer to your game, or to add social features like chat and Twitch integration. It has a visual scripting interface, but you'll get the most out of it if you're familiar with Lua or C++.
- Amazon have full set of videos to help you make your first ever multiplayer game with Lumberyard.
- There is also a 20 minute video about getting started with the tool.
- Get the tool here.