XSLTdoc is a Javadoc-like tool for all versions of XSLT (1.0, 1.1, 2.0). It defines conventions to document XSL "code elements" directly in the source code. These "documentation elements" are then extracted by the XSLTdoc tool to build a documentation consisting of several linked HTML pages which provide easy browsing through the documentation. The XSLT source code is available with syntax highlighting. It is freely available on a GPL licence. (cited from the project homepage)
This is not a tool for managing TEI but rather something that helps maintain the XSLT scripts that handle your TEI – for example, Sebastian Rahtz's XSL stylesheets for TEI XML used to be documented with XSLTdoc.
The software is written in XSLT 2.0 and installing it should take seconds, because all you have to do is unzip the archive. In order to configure it, you have to edit a pre-filled XML config file, setting the paths to suit your system. Documenting your XSLT is a matter of inserting <xd:doc> elements into your stylesheets. Then you need to run e.g. Saxon (packaged with the distribution) on xsltdoc.xsl (the root stylesheet), which produces a set of HTML files in a directory of your choice. CSS stylesheets are also provided and easily customizable.