XSL

Jade
An early implementation of an XSL processor. Converts XSL to DSSSL to render XML.
http://www.cogsci.ed.ac.uk/~ht/xslj.html

Jeni's XSLT Pages
Jeni Tennison is a very active XSLT community member. This page is her homepage for her many XSLT activities. With 25 tutorials/articles and 2 utilities for visitors. Good website.
http://www.jenitennison.com/xslt/index.html

NIST Toolbox
Collection of tools to make enable XML applications to interchange data easier. Includes APEX and ATTS.
http://www.mel.nist.gov/div826/staff/lubell/xsltoolbox/

TopXML XSLT Zone
With 34 original articles, the XSLT Zone explains XSLT in various solutions - such as .NET, mobile solutions and in applications. These articles range from introductory to advanced; through to tutorials and include complete XSLT and XPath references.
http://www.topxml.com/xsl

UWOBO XSL Processor
Invoked via URL giving the URI of an XML document and a list of stylesheets to be applied. Requires Tomcat and Xerces/Xalan.
http://helm.cs.unibo.it/uwobo/

XML Cover Pages: Extensible Stylesheet Language (XSL)
Introduction, history, articles and software support by Robin Cover. (Oasis)
http://xml.coverpages.org/xsl.html

XSL Lint
A semantic lint checker for that detects poor syntax and redundant areas of a stylesheet.
http://nwalsh.com/obsolete/xslint/

XSL Transformations (XSLT) Version 1.0
This specification defines the syntax and semantics of XSLT, which is a language for transforming XML documents into other XML documents. (W3C Recommendation 16 November 1999)
http://www.w3.org/TR/xslt

XSLT Requirements Version 2.0
This draft document describes the requirements for the XSLT 2.0 specification. (W3C Working Draft 14 February 2001)
http://www.w3.org/TR/xslt20req