OWLSharp

OWLSharp is a .NET library built atop RDFSharp with the goal of enabling semantic expressivity for:

Modeling OWL2 ontologies (entities, expressions, axioms, annotations, rules, ...)
Exchanging them using standard OWL2 formats (OWL2/XML)
Reasoning on them with a set of 25 OWL2 inference rules
Validating them with a set of 29 OWL2 analysis rules

It also integrates a powerful SWRL engine for modeling, exchanging and executing custom inference rules

Along with core ontology features, it also includes a set of extensions providing additional capabilities:

Create and validate schemes describing, documenting and organizing vocabularies of concepts (SKOS)
Model and analyze features having a spatio-temporal representation (GeoSPARQL, OWL-TIME)