Great alternative if you don't need the entire Office suite of applications.
"OpenOffice.org is the open source project through which Sun
Microsystems is releasing the technology for the popular StarOffice
productivity suite. It is an international office suite that will run
on all major platforms and provide access to all functionality and data
through open-component based APIs and an XML-based file format. It
establishes the necessary facilities to make this open source
technology available to the developer community." 
