OpenOffice is essentially a free Microsoft Office alternative. Its user interface is very similar to Office 2000 (i.e. ugly but serviceable). Unlike Office, it features a drawing program and direct support for PDF.
Mac users may wish to compare NeoOffice, which is a more Mac-like implementation of OpenOffice which, unfortunately, lags behind OpenOffice in functionality. The developers of NeoOffice have joined the OpenOffice team and a future version of OpenOffice will, apparently, have the Mac-like-ness of NeoOffice and be up-to-date.
http://openoffice.org/