http://razor.occams.info/code/semweb

SemWeb.NET is a Semantic Web/RDF library written in C# for Mono or Microsoft’s .NET. The library can be used for reading and writing RDF (XML, N3), keeping RDF in persistent storage (memory, MySQL, etc.), querying persistent storage via simple graph matching and SPARQL, and making SPARQL queries to remote endpoints. Limited RDFS and general-purpose inferencing is also possible. SemWeb’s API is straight-forward and flexible. (What is RDF?)