Most flexible Javascript framework for working with RDF?

What Javascript framework(s) do people use when working with RDF data? I'm aware of various SPARQL client libraries, rdfQuery and tabulator, but I'd like to get a sense of which frameworks offer the most flexibility, e.g. ability to parse and manipulate RDF locally on the client.

Very few Javascript clients handle RDF that I found, and none at scale. There are two basic problems: the first is limited computing resources, though Javascript interpreters have been getting better in recent years (particularly Chrome). The second problem is cross-domain security policies. Unless your Javascript client code and the data you want to process are in the same domain, you either need to a data source that supports JSON-P, or you need to use your own proxy to handle the transactions with the remote data-hosts. As Dave said, once you have an architecture that includes a proxy, you may as well use it for the heavy SPARQL/RDF lifting, and leave the client-side Javascript to focus on presentation.

That said, if I had to pick a client-side RDF library, rdfQuery would be the obvious choice ... though it doesn't include an RDF parser.

Not a direct answer to your question but we had considerable success using plain jQuery working on top of the linked data api, by exploiting the JSON encoding that that gives out of the box, leaving the RDF to the server (or in our case proxy) to handle. We were able to build browsing functions and visualizations (using GoogleMaps and GVT) over Edubase and other data with pretty little effort.

Franz recently announced JavaScript for Stored Procedures for use with its Allegrograph triple store. From my quick scan of the docs, it looks like JavaScript can be runnable by clients or installed at the server to run as a stored procedure.