From the site:

SemWebCentral is an Open Source development web site for the Semantic Web. It was established in January, 2004 to support the Semantic Web community by providing a free, centralized place for Open Source developers to manage Semantic Web software and content development. Another purpose is to provide resources for developers or other interested parties to learn about the Semantic Web and how to begin developing Semantic Web content and software.

Tools for Semantic Web Rules and Ontologies, including Translation, Inferencing, Analysis, and Authoring.

From the site:

The Semantic Web Education and Outreach (SWEO) Interest Group has been established to develop strategies and materials to increase awareness among the Web community of the need and benefit for the Semantic Web, and educate the Web community regarding related solutions and technologies. 

A very concise and straightforward introduction to XML, RDF and the Semantic Web.

Updated Sept 7 2008: added seaBreeze link

Seaside

To get a good feel for Seaside development environment, read the excellent technical introduction by Shaffer Consulting.

Note that the article was written in 2005 and may be obsolete in parts. For example, Seaside now supports several object-oriented databases, including Gemstone.

Link to the LSDIS (Large Scale Distributed Information Systems) Lab

From the W3.Org site

The Open Data Movement aims at making data freely available to everyone. There are already various interesting open data sources availiable on the Web.

REWERSE is short for "Reasoning on the Web with Rules and Semantics".

From the site: REWERSE is a research "Network of Excellence" (NoE) on "Reasoning on the Web" that is funded by the EU Commission and Switzerland within the "6th Framework Programme" (FP6), Information Society Technologies (IST), Priority 2 under the project reference number 506779. REWERSE addresses the IST strategic action line "Semantic-based knowledge systems".

Mike Bergman's site has an interesting article on ESW, titled "Enterprise Semantic Webs (ESW) Demand New Database Paradigms", at http://www.mkbergman.com/?p=185. In fact, it's one of the few defintions of ESW availible.

SemSol seems to be connected to the Semantic Web Community Portal, http://www.semanticweb.org/, which has been on the verge of being relauched for many months ....

From the SemSol site, "SemSol is a forthcoming Web development framework that uses Semantic Web technology to significantly increase productivity and flexibility for everyday Web programming".

Also see http://bnode.org/, Benjamin Nowack's personal website.

The Inference Web is a Semantic Web based knowledge provenance infrastructure that supports interoperable explanations of sources, assumptions, learned information, and answers as an enabler for trust.

From the About CSAIL page:

The primary mission of CSAIL ( Computer Science and Artificial Intelligence Laboratory ) is research in both computation and artificial intelligence, broadly construed. It is organized into four broad research areas:

Systems covers all aspects of the building of both hardware and software computational systems

Perception and Learning includes work on the sorts of things that all people manage to do effortlessly, both emulating those abilities, and simulating their appearance.

Mike Bergman has written numerous insightful articles about the Semantic Web.

Link to BB.COM SOA Subject

Semantic web tutorial ( Static HTML ).