The Simile folks have released Longwell, their RDF browser suite. Looks good. It's a web application, but it's not clear that there's a web-services access point. Clearly, for a tool that's primarily user-facing, having a web-service endpoint is less relevant. But from first impressions, I would guess that some of Longwell's reasoning and storage capabilities would be useful components in a more general loosely-coupled semantic web application.