http://triplify.org/Overview Written in PHP, LGPL license.
They encourage implementing in other languages.
Triplify provides a building block for the “semantification” of Web applications. Triplify is a small plugin for Web applications, which reveals the semantic structures encoded in relational databases by making database content available as RDF, JSON or Linked Data.
Triplify is very lightweight: It consists of only a few files with less than 500 lines of code. For a typical Web application a configuration for Triplify can be created in less than one hour and if this Web application is deployed multiple times (as most open-source Web applications are), the configuration can be reused without modifications.
Triplify makes Web applications easier mashable and lays the foundation for next-generation, semantics-based Web searches.