Wow check out the latest article on Lifehacker. The version of LibreOffice can work with DocX files.
Windows/Mac/Linux: The first finalized release of the OpenOffice.org spin-off, LibreOffice, has hit the web at version 3.3. It’s got a few unique features, an ever-so-slightly tweaked look, and the ability to export to Microsoft’s DOCX format by default.
You can read up on the new features and fixes and general release notes, but know that, in general, this is an OpenOffice.org package released under a different banner, for a multitude of reasons.
LibreOffice is a free download for Windows, Mac, and Linux systems. Note the “Download with BitTorrent” checkbox when you’re downloading, and use it if you can—my download was quite slow this morning.