An optimizing XSLT compiler for Java, which turns stylesheets into binary Java classes.

Unsupported XSL processor written in Java, using the Simple API for XML (SAX 1.0) and the Document Object Model (DOM 1.0) API. This package also contains xslSlideMaker, a post-processor that can quickly make slides and multi-level slides with XML & XSL. The Koala XSL engine is no longer supported - but the source is available.

Libxslt is the XSLT C library developed for the Gnome project. Libxslt is based on libxml2 the XML C library developed for the Gnome project. It also implements most of the EXSLT set of extensions functions and some of Saxon's evaluate and expressions extensions. People can either embed the library in their application or use xsltproc the command line processing tool. This library is free software and can be reused in commercial applications (see the intro). Includes a link to a tutorial.

PSGML is a GNU Emacs Major Mode for editing SGML and XML coded documents. PSGML has several functions for editing SGML documents. Indentation according to element nesting depth and identification of structural errors (but it is not a validating SGML parser). Menus and commands for inserting tags with only the contextually valid tags. Attribute values can be edited in a separate window with information about types and defaults. Structure based editing includes movement and killing; and also several commands for folding editing.

A package collecting the tools required for writing basic XML applications in Python, along with documentation and sample code. Features include (but are not limited to) SAX, DOM, the xmlproc validating parser, and an Expat interface.

SAXON is an XSLT processor developed by Michael Kay.

The Schematron is an XML structural validation language that uses patterns in trees instead of being based on grammars. Tested to work with the following XSLT implementations: MSXSL, SAXON and Oracle work fine. XT, Xalan, and Sablotron can work with certain caveats. Plenty of source code.

A couple of online utilities for converting XML and DTDs to XSL.

Commercial IDE for creating, validating, and debugging XSL, and XML-to-XML mappings. Integrated XSLT, Java, and MSXML debugger.

Tool to debug XSL transformations which is part of Stylus Studio. [Commercial]