RACER is a Semantic Web inference engine for developing ontologies query answering over RDF documents and wrt. specified RDFS/DAML and OWL ontologies registering permanent queries (e.g., for building a document management system) with notification of new results if available (publish-subscribe facility).RACER is a Description Logic reasoning system with support for TBoxes with generalized concept inclusions ABoxes Concrete domains (e.g., linear (in-)equalities over the reals) RACER is a prover for modal logic Km with graded modalities and axioms.The Racer system is a knowledge representation system that implements a highly optimized tableau calculus for a very expressive description logic. It offers reasoning services for multiple TBoxes and for multiple ABoxes as well.The system implements the description logic ALCQHIR+ also known as SHIQ. This is the basic logic ALC augmented with qualifying number restrictions, role hierarchies, inverse roles, and transitive roles. In addition to these basic features, RacerPro also provides facilities for algebraic reasoning including concrete domains for dealing with: min/max restrictions over the integers, linear polynomial (in-)equations over the reals or cardinals with order relations nonlinear multivariate polynomial (in-)equations over complex numbers, equalities and inequalities of strings