ah, it's not super interesting. Most EMR systems provide an open list of FHIR endpoints for their customers. `fasten-source-gen` is basically an ETL repository which imports the endpoint metadata provided by these EMR systems and enriches it with data from NPPES, Google Maps, user contributed data, Mechanical Turk and elsewhere.
- Epic: https://open.epic.com/MyApps/Endpoints - Cerner: https://github.com/cerner/ignite-endpoints
It will be open sourced (eventually) -- once I've cleaned up some test credentials that were inadvertently committed to the repo.
Hope that answers your question?