From The Apache Software Foundation:
Apache OpenOffice is both an open-source product and a project. The product is a multiplatform office productivity suite. It includes desktop applications such as a word processor, a spreadsheet program, a presentation manager, and a drawing program, with a user interface and feature set similar to those of other office suites. OpenOffice.org also works transparently with a variety of file formats, including those of Microsoft Office. Localizations of OpenOffice.org are available in 27 languages, with more being constantly added by the community. OpenOffice.org runs on Solaris, Linux (including PPC Linux), and Windows. Written in C++ and with documented APIs licensed under the LGPL and SISSL open-source protocols, OpenOffice.org allows any knowledgeable developer to benefit from the source.