OpenOffice.org (OOo), commonly known as OpenOffice, was an open-source office suite. It was an open-sourced version of the earlier StarOffice, acquired Sun Microsystems Sun open-sourced the software as a competitor to Microsoft Office. The project was closed by Oracle Corporation, the then-owner of Sun. Active successor projects include Apache OpenOffice, LibreOffice and NeoOffice.

OpenOffice.org's default file format was the OpenDocument Format (ODF), an ISO/IEC standard, which originated with OpenOffice.org. It could also read a wide variety of other file formats, with particular attention to those from Microsoft Office.