What is ODS?
LibreOffice and OpenOffice's spreadsheet, and the ISO-standard one - the same ODF packaging an ODT uses, with sheets where a document has pages. Every cell stores its value and, separately, the text shown for it, which is why a figure formatted as currency can still be read back as the number underneath.
What is Markdown?
Plain text with just enough punctuation to imply formatting, which is why it ended up as the default for READMEs, issues, wikis and notes. Its tables are the awkward part - a pipe-and-dash grid that's readable enough written by hand and tedious to maintain by hand.