From Scruffy Software:
FOEditor is an application for editing Formatting Objects within XSL Transformations (XSLT) documents. FOEditor can transform an XML document into a Formatting Objects document which can be converted or saved in Portable Document Format (PDF) or Rich Text Format (RTF). PDF transformations can be previewed either internally or externally with the default PDF viewer.
FOEditor is also a general purpose XML document transformer. Simply select XML and XSLT documents. XHTML transformation results can be preview in the default browser.