Resource Description Framework is a W3 initiative toward the semantic web - http://www.w3.org/RDF/
Redland is a library that provides a high-level interface for RDF allowing the RDF graph to be parsed from XML, stored, queried and manipulated. Redland implements each of the RDF concepts in its own class via an object based API, reflected into the other language APIs - Perl, Python, Tcl, Java and Ruby. Some of the classes providing the parsers, storage mechanisms and other elements are built as modules that can be added or removed as required. See http://librdf.org/docs/tcl.html . Now Redland librdf RDF API Library is no longer supported C#, Java and Tcl bindings.
SC As part of CANTCL and more recently giggle I've built a simple RDF triple store [L1 ] which stores things in a metakit database. Currently this supports only the most trivial of RDF-like applications but it will grow as I use it some more. Note this doesn't parse any RDF serialisation, it just stores triples.
http://microformats.org/ is a project defining various standard markups which can be embedded into web pages.
GraMToR (Graphical Modeling Tool for RDF) is a graphical Editor for RDF models.