SWI-Prolog is a free implementation of the programming language Prolog, commonly used for teaching and semantic web applications.It has a rich set of features, libraries forconstraint logic programming,multithreading,unit testing,GUI,interfacing to Java, ODBC and others,literate programming,a web server,SGML, RDF, RDFS,developer tools (including an IDE with a GUI debugger and GUI profiler), and extensive documentation.SWI-Prolog runs on Unix, Windows, Macintosh and Linux platforms.SWI-Prolog has been under continuous development since 1987.