This format is used to do spreadsheets with Excel 2007 and later. It has the ods format as an open equivalence.
Name : PowerPoint Microsoft Office Open XML Format Spreadsheet
Mime : application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Licence : Proprietary
Type : Spreadsheet document
Free softwares to open ppsx : LibreOffice Calc
Non free softwares to open ppsx : Microsoft Excel 2007 and later