The official Retsly Node.js SDK by Retsly calls the Retsly API which provides access to Retsly's real state backend. It can be used to build robust realtime applications without a database. Currently, this is SDK version 2.
One of the challenges with building an application these days is the number of dependencies that application will actually have on other applications. Ideally in order to know how that application will actually perform application developers would be able to test their application against the application it depends on running in production. The odds of that happening, however, are slim to none, especially if that other application is running as a cloud service that has to be always available to end users.