Two proof-of-concept implementations of a Web Prolog node are available, both written in SWI-Prolog. They exist to demonstrate that the ideas described in the book are realizable, not to serve as production-ready systems. Neither is complete, and both should be read in conjunction with the book.
This implementation is written for clarity. The code is meant to be read alongside the book, and every design decision maps directly to a concept described there. As a result, a number of features are absent or only partially sketched out. It is the right starting point if your goal is to understand how Web Prolog nodes work from the inside.
This implementation has been developed with breadth in mind. It covers a considerably larger portion of the language and protocol, including features that the transparent node deliberately omits. The code is more involved, and less suited as a first read, but it gives a more realistic picture of what a functioning Web Prolog node looks like in practice. Some features remain unimplemented here as well.