Hi Arne, this looks great & useful!
The m-ld JavaScript engine is a component for sharing RDF graphs among multiple peers, including browser clients. Its like having a local graph that can be collaboratively edited. It has an RDF/JS API! (Example)
I have often wondered whether it would be useful purely as a local graph library, without the sharing stuff. In fact, the only change would be to make the connection to remote replicas fully optional… I’d love to know if that would be of interest (contact details here, to avoid a thread hijack!).