And many more ...

See also:

• Semantic Web testimonials from enterprise-scale implementors and independent developers illustrate current uses of RDF / OWL on the Web today.
• Implementation report for the RDFCore Working Group
• Implementation report for Web Ontology Working Group

These highlight a large and growing number of products and open source tools and toolkits (Parsers, Reasoners, APIs, etc.) in various languages (Java, Lisp, Python, PHP, Perl, C, C#, etc.)

Personal favorites I use on a weekly (daily) basis - Jena2 (java) and RDFlib (python)