Backendless is a key value store that allows data in JSON format to be stored on Amazon S3 (Simple Storage Service). It is built on top of Node.js in order to achieve fast performance and scalability.
The advantage of using Backendless is that data is stored on your own Amazon S3 account and not on ours. The Node.js server ensures that data is stored / retrieved fast and efficiently from S3.
Why? We think the answer can be pretty much found on this article from Pete Warden (a 2010 article that describes the advantages of using S3 as a key value store).
We are planning on releasing a .NET library soon too, compatible with Xamarin and also for Window Phone. The library will also work for desktop .NET apps and ASP.NET apps / sites.