AbiWord is a free word processing program under the GPL which runs on Linux, MacOS and Microsoft Windows. There is basic formatting as well with styles but no table support at the moment. It has a wealth of import/export formats like RTF, HTML and LaTeX. The native file file format is XML, so documents written with the program are a safe investment from the point of view of digital archiving.
Latest release of Abiword contains Wikipedia plugin.
Link: