Amazon's releasing their very own game engine. Lumberyard, as they call it, is based on Crytek's famous CryEngine, and can be used to develop games for both PC and consoles. It's also free to download, and comes with "no seat fees, subscription fees, or requirements to share revenue". Fees come in only, as Lumberyard's official page notes, if the game takes advantage of the engine's integration with Amazon Web Services for multiplayer. Besides AWS, the engine has specific features which target Twitch:
With Amazon Lumberyard's Twitch ChatPlay, you can use a drag-and-drop visual scripting interface to create gameplay features in as little as minutes that let Twitch viewers use chat to directly impact the game they are watching in real-time. And, the Twitch JoinIn feature within Amazon Lumberyard helps you build games that let Twitch broadcasters to instantly invite their live audiences to join them side-by-side in the game, with a single click, while others continue to watch.
While the engine is based on Crytek's CryEngine, which Amazon licensed last year, Lumberyard will, as general manager Eric Schenk put it (via Gamasutra), "go in [its] own direction." He added that at launch, the engine already has components that are not based on CryEngine, including low-latency networking code and "an entirely new asset pipeline and processor."
It's particularly noteworthy that the engine is completely free. If you look at its competitors, like Unity, Unreal Engine 4 or even CryEngine itself, for example, all of them come with either a licence fee or a royalty fee.
Lumberyard, which is currently in beta, can be downloaded here.