You can use TextEdit (included with OS X), it has support for
rtfd (with attachments, e.g. images),
odt (OpenDocument from OpenOffice), and some support for
There's Microsoft Office for Mac, of course, with full support for
docx (macros might not work though, check the MS documentation). Word also supports
rtf of course.
OpenOffice / LibreOffice / NeoOffice support
docx quite well too, AFAIK, but their native format is
odt. They also support
Apple sells iWork with Pages, whose native format is
.pagesand incompatible with everything else.
There are a few other word processors with fewer users, like Mariner Write, but I don't know about their file format support.