XML Nanny is a free Cocoa application for Mac OS X that allows you to parse and validate local or remote XML documents against DTD, W3C XML Schema, RELAX NG, and Schematron schemas.

AquaPath is a free Cocoa-based developer tool for Mac OS X that allows you to evaluate XPath 2.0 expressions against any XML document and view the result sequence in a dynamic, intuitive tree representation.

The suite of Automator Actions for Mac OS X that brings drag-and-drop simplicity to creating and automating complex XML Processing Pipelines.’

The OttoMate Actions serve as an engine for Apple’s best-of-breed web browser, Safari