A VERY STRONG RIVAL TO MICROSOFT OFFICE
Apache OpenOffice is an open-source office productivity software suite containing word processor, spreadsHeet, presentation,graphics, formula editor, and database management applications. It was formerly known as OpenOffice.org under Sun, thenOracle ownership. OpenOffice's default file format is the OpenDocument Format (ODF), a ISO/IEC standard. It can also handle other file formats including those from Microsoft Office. OpenOffice runs on several operating systems. As of June 2011, it supports over 120 languages. It is distributed under the GNU Lesser General Public License and Apache License open source licenses.
You can download Apache OpenOffice from here