The Wiki article on the Open Document Format (ODF) might be worth reading. The ODF is ISO/IEC 26300:2006 with Amendment 1 in 2012. ODF is also called just OpenDocument.
Early in the Wiki:
The specifications were originally developed by Sun Microsystems as an XML format for OpenOffice.org office suite.
Well down in the Wiki, I found:
The free office suites Apache OpenOffice, Calligra, KOffice, NeoOffice and LibreOffice all use OpenDocument as their default file format.
ODF has been at least partially supported by MS Office 2007 (service pack 2) and newer..