Microsoft announced in November 2005 that it would co-sponsor standardization of the new version of their XML-based formats through Ecma International as 'Office Open XML'. The Excel and Word formats-known as the Microsoft Office XML formats-were later incorporated into the 2003 release of Microsoft Office. In 2002, a new file format for Microsoft Word followed. In 2000, Microsoft released an initial version of an XML-based format for Microsoft Excel, which was incorporated in Office XP. Microsoft Office 2013 and later fully support ISO/IEC 29500 Strict, but do not use it as the default file format because of backwards compatibility concerns. Microsoft Office 2010 provides read support for ECMA-376, full support for ISO/IEC 29500 Transitional, and read support for ISO/IEC 29500 Strict. ISO and IEC standardized later versions as ISO/IEC 29500.

Ecma International standardized the initial version as ECMA-376. Office Open XML (also informally known as OOXML) is a zipped, XML-based file format developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents.

Open office for windows