What LibreOffice, OpenOffice and Google Docs save a document as, and the ISO-standard counterpart to .docx. Inside it is a zip of XML, which is the reason a table drawn in one can be read back out at all. It is a page format first - paragraphs, page breaks, headers, footnotes - so the only part of it that is data is a table someone drew on the page.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop an ODT file above and choose afterwards.