The main tool of my research is semantic Web services, and specifically, semantic Web services written in OWL-S. As I am explaining quite a lot about them, I hope to refer them to this text instead 
OWL-S (formerly DAML-S), is a Web Description Language (OWL) based ontology for semantic Web services. Web Services are automated resources accessed via the Internet, using a standard XML interface, described by a Web Services Description Language (WSDL) specification.
OWL-S describes the properties, capabilities and process model of a Web service. It enables Web services to be discovered, interoperated and composed in an “unambiguous, computer-interpretable form”. OWL-S elements can be mapped to a WSDL specification, in order to support automatic invocation and execution of a Web service, according to its OWL-S description.
Among other things, OWL-S augments the Web service’s specification methods by using semantic notation of resources which can be inputs, outputs, effects and preconditions. The semantic notation is based on standards that form the vision of the Semantic Web. The Semantic Web is “an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation.” (From: Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001). The Semantic Web vision is materialized by several languages that are used to describe knowledge: RDF, RDF Schema and OWL, to name the significant ones.
The latest release of OWL-S is OWL-S 1.1. Several resources can help learning about OWL-S. The technical overview is a good start. Several examples are avaliable, as well as formal definition written in OWL. The most noted publication regarding OWL-S is DAML-S: Web Service Description for the Semantic Web”, The First International Semantic Web Conference (ISWC) (PDF). Other publications can be found here.
By the way, there are more languages for describing semantic Web services, such as WSMO, WSDL-S and others. As their core capabilities are similar to OWL-S and they gained less interest from the research community, I do not discuss them here.
In my opinion, the Web Service Composer is the most notable tool demonstrating the capabilities of OWL-S. It enables dynamic composition of a Web service from other Web services, according to their OWL-S (well, DAML-S) descriptions. Semantic relations are used in order to help the designer match and compose the services. Another important application is the OWL-S API that enables Java access to OWL-S descriptions. Both applications are from Mindswap lab.
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