Amazon Sumerian lets you create and run virtual reality (VR), augmented reality (AR), and 3D applications quickly and easily without requiring any specialized programming or 3D graphics expertise. With Sumerian, you can build highly immersive and interactive scenes that run on popular hardware such as Oculus Rift, HTC Vive, and iOS mobile devices (support for Android ARCore coming soon). For example, you can build a virtual classroom that lets you train new employees around the world, or you can build a virtual environment that enables people to tour a building remotely. Sumerian makes it easy to create all the building blocks needed to build highly immersive and interactive 3D experiences including adding objects (e.g. characters, furniture, and landscape), and designing, animating, and scripting environments. Sumerian does not require specialized expertise and you can design scenes directly from your browser.
In other words, Sumerian is a direct competitor to Sansar, High Fidelity, Decentraland, and every other would-be VR platform enabling user-generated content for VR experiences.
Unless I missed it, the only differentiator High Fidelity et. al. can now offer is monetization through virtual currency. However, Amazon could easily add direct in-app payment monetization via payments for content from anyone with a credit card registered on Amazon (which basically means roughly half of everyone on the Internet), or indirect monetization through Amazon affiliate codes. (I.E., Click on some virtual furniture depicted in a Sumerian experience, get taken directly to the Amazon web page where you can buy a real world copy of that same piece of furniture.)
The other advantage Amazon Sumerian has is that virtual experiences created on it are hosted on Amazon Cloud Services:
As with many other AWS services, Sumerian is “free” to use: you pay only for the storage for what you create.
Sumerian's leading competitors either use AWS themselves or have a cloud service option -- High Fidelity recently announced a partnership to do just that. But AWS is the industry gold standard. In other words, competition among VR platforms just got a lot more fierce -- while their future got a lot more cloudy. (See what I did there?)