A file with .fodt extension is a text document saved in OpenDocument flat XML file format. Contrary to .odt files, which are saved in .zip container file format, the FODT files are stored to disc as human readable files that can be opened in any text editor for viewing as plain XML documents. The OpenDocument office document standard was developed by the OASIS industry consortium, paving a way for anyone to implement by anyone without any restrictions. Other popular OpenDocument file formats include .odt, .ott, .ods, .odp, and similarly others.
FODT File Format - More Information
FODT files are stored in plain XML file format (also known as Flat XML or Uncompressed XML), though it is not commonly used document format by OpenDocument. OpenDocument files are commonly saved as a ZIP package, consisting of a number of files and directories. The XML based OpenDocument files may not be supported on some software and that is why their use is less common as compared to the ZIP package based files.