eXist-db is a feature rich Open Source native XML database
eXist-db is a native XML database featuring efficient, index-based XQuery processing, extensions for keyword search, XUpdate support, XSLT support, XForms support, REST and tight integration with existing XML development tools. Moved to Github - https://www.github.com/exist-db/exist
"xmlsh" is derived from the design and goals the unix shell and core commands but with XML expressions and documents added as core features to the shell. xmlsh can be used as a drop-in replacement for scripting xml transformations instead of sh.
Everything is XML - Everything is possible - Keep it simple
WebPath is an experimental implementation of XPath 2.0 in Python, initially developed during Yahoo! Hack Day. It uses a novel parsing technique called Top Down Operator Precedence. Seeking developers to improve implementation and conformance.
XIPL/XASM is a basic environment to build high-level Image Processing operations using a XML-based language. The idea is to compile the high-level XIPL language into a low-level one, XASM (XML-based too), using XSLT technology.