Updated Sept 24 2008: added features and SWCL link

From the site:

The Semantic Web Client Library represents the complete Semantic Web as a single RDF graph. The library enables applications to query this global graph using SPARQL- and find(SPO) queries. To answer queries, the library dynamically retrieves information from the Semantic Web by dereferencing HTTP URIs and by following rdfs:seeAlso links. The library is written in Java and is based on the Jena framework.

Update 3/26/2008 - ARC completely reimplemented and released as ARC2.

Update 7/25/2008 - added Triplify 0.3 section.

From the ARC site:

ARC is a lightweight, SPARQL-enabled RDF system for mainstream Web projects. It is written in PHP and has been optimized for shared (or otherwise performance- or privilege-limited) Web environments.

ARC facilitates the integration of RDF and SPARQL functionality in PHP/MySQL-driven frameworks.

Updated: Sept 24 2007

It is a browser plugin, which introduces browser dependencies, but the project is Open Source and seems to be active and well-supported.

From the site:

Mozilla RDF was originally used to support the Aurora/Sidebar user interface and SmartBrowsing metadata services. It's main use in Mozilla now is as a common data model and API for use in XUL-based applications.

Revised Nov 1 2008: Draft of OWL2 specs.

The recent drafts of the OWL2 specification describe some important changes from OWL1. In a nutshell,

The structural specification of OWL 2 provides the foundation for the implementation of OWL 2 tools such as APIs and reasoners. ... This document also defines the functional-style syntax, which closely follows the structural specification and allows OWL 2 ontologies to be written in a compact form.

Potential RDF use cases for Drupal - an excellent article about RDF in Drupal 6 - 7.

The Drupal RDF module uses the recently-rewritten ARC2 RDF Library if available but apparently does not require it.

From the project page:

Node linking and Metadata

The Relationship Manager module is intended to allow free-form links between nodes, recording not just that one page relates to another, but HOW it relates. ... The core module is made available to be extended by other modules that wish to make use of the generalized relationship management functions. Several examples of simple modules that leverage this power are provided as optional plugins.

The major plugins are:

More pattern matching and structural parsing than symbolic processing in a classical sense of an inference engine.

Nov 4 2009: Getting active, or maybe reactivating.

This page is just a collection of links so far. The link above for the 'Miscellaneous' subject is to my own modest effort with Semantic Mediawiki.  It's nascent but coming along.

The entire Semantic Web subject area will be getting a makeover soon.

Weaving Meaning: An Overview of the Semantic Web

Good W3 Powerpoint presentation by Eric Miller.

Updated: Sept 10 2007

There is a small but persistent Smalltalk/OWL project. From their project information page:

The Smalltalk OWL Project was launched 1 Jan 06, the overview of the effort is:

A strong candidate for a Smalltalk RDF/OWL inference engine is the Smalltalk Open Unification Language (SOUL).

This is a new topic ... it is more abstract than most content on this site and may be moved to the Home site.

Of the 702 Semantic Web tools listed in Mike Bergman's masterlist, 332 are implmented in Java .... and Java now being a fully open source and open licence language ...

Stray link I'll find a home for: http://www.daml.org/tools/

SWCL - Semantic Web Client Library:

The preeminent tool for RDF parsing in Javascript must be the Tabulator project at CSAIL. The Tabulator 0.7 demo is fairly impressive and gives one a good sense of what RDF is about, but don't expect it to run quick. The new version 0.8 is over 200KBytes ( tgz-ippped ! ).

A MIT student did some work with a stripped-down version of the RDF parser to good effect.