Here is information about some of the tools mentioned in this book. If you are running Linux, you may be able to load some of these tools using a package manager like Synaptic, yum, or apt. Needless to say, this is not a comprehensive list; there are other capable tools available. However, these are a good starting place.
A variety of tools that support RELAX NG can be found at: http://relaxng.org/. These include:
Sun Multi-Schema XML Validator (from Sun Microsystems). MSV is an open source program that validates RELAX NG as well as other schema languages including W3C XML Schema.
An open source RELAX NG validator that supports both compact and XML syntax.
An open source program that is a companion to Jing, Trang converts between various XML schema languages. It supports both compact and XML syntax for RELAX NG, XML 1.0 DTDs, and W3C XML Schemas, though it only supports W3C XML Schemas for output.
This is an open source addon for emacs that supports syntax-directed editing using a RELAX NG compact mode schema. It validates as you type and will show you at any point what the valid set of elements, attributes, and attribute values is. It also supports automatic completion of partially typed elements, attributes, and attribute values.
Saxon is an XSLT processor. The basic processor is available as an open source product, and there are also commercial versions that offer additional features. The latest versions of Saxon support both XSLT 1.0 and 2.0.
Xsltproc is an open source XSLT processor that supports XSLT 1.0.
The <oXygen/> XML Editor is a popular commercial editor. The latest versions support DocBook V5.0, including both the RELAX NG and Schematron rules. It is also integrated with the DocBook stylesheets.
The XMLmind XML Editor is a popular commercial editor that comes in two varieties, a personal edition and a professional edition. The personal edition is free for non-commercial use. Both versions support DocBook V5.0.