The XPX file extension is used by Accessible FormNet program, developed by Intercom. Accessible FormNet™ allows a wide range of customers to digitally interact with other organizations using electronic forms to improve customer service and provide you with accurate data so vital to growing your business. A .xpx file contains form data. MIME: application/vnd.intercon.formnet
Some reference sites point to the use of .XPX as a form of XML file. While there are no specific programs mentioned, try opening the file in a text editor to see if it has the XML format (tags and data).
The XPX file extension is associated with XP-RAFTS2000, a non-linear runoff routing model used extensively throughout Australasia and South East Asia. RAFTS is the acronym for Runoff Analysis & Flow Training Simulation A .xpx file contains macroes used by all products in the XP software line.