Another video game engine has entered the world, this time from Amazon. It is basically a fork of CryEngine that they purchased the rights to sub-license. Amazon states that their engine will diverge over time, as they modify it in-house for licensees and their internal game studio, Amazon Game Studios. It is licensed for free, with full source access, but it has a few restrictions.
The market is currently dominated with a variety of offerings with different business models. Unreal Engine 4 is free to use, but takes a portion of revenue after some grace amount. CryEngine is available on a relatively cheap subscription, but has no royalty requirements. Unigine offers a few lump-sum options, starting at almost a grand-and-a-half. Unity has a few options, from a cut down free version, to a relatively expensive subscription, to lump-sum payments. Finally, at least for this list, Source 2 is completely free, with the only requirement that published games must be available on Steam at launch.
That last one, Source 2, is basically the business model that Amazon chose with their new Lumberyard engine. The difference is that, instead of requiring games to be published at a certain retailer, they require that games use Amazon Web Services for online interactions, like multiplayer and cloud, unless the developer maintains their own servers. I'm not exactly sure what that distinction ("If you own and operate your own private servers") allows, but I'd assume that Microsoft Azure and Google Cloud are big no-nos. On the other hand, single-player experiences and games with local multiplayer, assuming neither has “cloud” features, are completely free to make.
While it would be nice to have a purely open source offering that can compete with these proprietary engines, developers should be able to find a suitable option. Each seems to ask for something slightly different, and they are very permissive otherwise.