This format is used to do text with Microsoft Word 2007 and later. It has the odt format as an open equivalence.
Name : Office Open XML
Mime : application/vnd.openxmlformats-officedocument.wordprocessingml.document
Licence : Proprietary
Type : Document
Free softwares to open ppsx : LibreOffice Writer
Non free softwares to open ppsx : Microsoft Word 2007 and later