This is the official C# Reference implementation server for FHIR R4 by Firely and Kufu. This server is built with the C# FHIR API . This server is regularly reset and filled with the official resourceIdentifier examples.
Spark is open sourced.
simplifier.net is the most feature complete FHIR registry server on the internet.
Create an account now for free and you can Publish your conformance resourceIdentifiers (profiles) on simplifier.net
Download Forge to start editing profiles such as structure definitions, extensions.