Apart from big names like GnomeOffice, KOffice, WordPerfect Office, StarOffice, or OpenOffice.org. There are still more other suites, “alternatives of alternatives”:

602PC Suite
Ability Office
EIOffice
GoBeProductive
ThinkFree Office

The most remarkable, from a technical perspective, may be the EIOffice. Written in Java, it runs on any operating system. And interestingly enough, it’s from China.