The
WebServicesFaq links to a couple BPEL implementation, and a few introductory articles.
E.g., it links to the BPWS4J implementation, which -although outdated now- works fine, and is about the easiest way to get started with BPEL. It requires nothing more than a
servlet container, and includes example web services.
There's also a link to Apache ODE, which is another BPEL implementation as a web app, and which is still being developed (BPWS4J is not).
[ September 17, 2007: Message edited by: Ulf Dittmer ]