OpenOffice.org (also referred as OO.o or OOo) is an office application suite available on several different operating systems.
OpenOffice.org was initially created by a company called StarDivision in Germany under the name "StarOffice". The source code of this application was later acquired by Sun Microsystems in August of 1999. To reduce the overwhelming market share of Microsoft Office, the code of StarOffice was released to the public in July of 2000. By doing this, Sun Microsystems offered a free and open alternative to Microsoft Office.
Since the trade mark of OpenOffice was already taken, they chose the name OpenOffice.org and that is why the open version of StarOffice is "unofficially" called OpenOffice.
Sun Microsystems partially funds the development of OpenOffice.org and uses it as a base for its commercial version of OpenOffice(i.e. StarOffice) and also includes few additional components to make the StarOffice worth buying.
Based on its mission statement, the goal of OpenOffice.org is "To create, as a community, the leading international office suite that will run on all major platforms and provide access to all functionality and data through open-component based APIs and an XML-based file format."
The OpenOffice.org Suite has the following components:
A word processor with the same look and feel of Microsoft Word.
A spreadsheet application similar to Excel.
A presentation program like Microsoft PowerPoint.
A vector-based graphics and drawing tool.
A database management and manipulation tool like Microsoft Access.
A tool for creating and editing mathematical formulae.
OpenOffice.org pioneered the ISO/IEC standard OpenDocument file formats (ODF), which it uses natively, by default. It also supports reading (and in some cases writing) a large number of legacy proprietary file formats (e.g. WordPerfect, StarOffice, Lotus software, MS Works, Rich Text Format), most notably including Microsoft Office formats.