The X-Function technology (available since Origin 8) provides a framework for building Origin tools. In fact, most of Origin's revamped and greatly-expanded lineup of analysis and data processing tools have been implemented using this new technology.
Origin ships with many X-Functions that are saved on disk in XML file format, with extension .OXF. These System X-Functions are located in the \X-Functions subfolder of the Origin program folder. There is a separate help file that contains detailed information on built-in X-Functions (Help: X-Functions).