The DITA Open Toolkit is an implementation of the OASIS DITA XML Specification. The Toolkit transforms DITA content into many deliverable formats. See http://dita-ot.sourceforge.net/ for documentation and links to downloads. The source code and issue trackers have been moved to https://github.com/dita-ot/dita-ot
The Eclipse XML Meta-Modeling Tools project provides tools like editors, extended validation and generators for developing xml based meta-models and domain-specific languages in eclipse.