Most productivity suites based on OpenDocument schema, such as OpenOffice.org, LibreOffice, NeoOffice etc. should be able to convert ODT documents to other similar formats, including OpenDocument Flat XML files (.fodt). This can be done simply by using the File ► Save as.. program menu option.
Convert ODF text document to OpenDocument Flat XML document.
We have found 3 software records in our database eligible for .odt to .fodt file format conversion.
Apple macOS / Mac OS X software - convert odt to fodt on OS X
A full-featured set of office applications for Mac OS X
Convert from odt file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned odt to fodt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Multiplatform software - convert odt to fodt on any platform
Word processor and text editor from OpenOffice.org suite
Full-featured word processing and desktop publishing tool from LibreOffice suite