Saving ODT in MS Word
Click File→Save As→OpenDocument Text.
Saving ODT in Office 365 Online
Click the File tab→Save As→Download as ODT.
Please, not the differences between the OpenDocument Text (.odt) format and the Word (.docx) format used by Word Online.
Saving ODT in WPS Office
Install ODF plugin — ODF add-in for WPS Office. Click File→ODF→Save As ODF.