FODT is a special type of XML-based OpenDocument format used in OpenOffice.org Writer and similar tools and most users are actually not familiar with that and often wonder how to open or export these files to some alternative format, for example RTF - Rich Text Document format, which is what fodt to rtf conversion describes.
You can simply download OpenOffice.org or LibreOffice bundles and use the word processor (Writer) to resave the .fodt documents as .rtf files.