I've put some work into [`RDF::Blazegraph`](https://github.com/no-reply/rdf-blazegraph) as a possible recommended backend. I believe the requirements are: - Quad support - Safe blank node handling - Efficient read/update of individual named graphs It would be nice to have a fully public domain backend but `Rack` and `Sinatra` are under MIT, either way.