This just in: None of them matter commercially. Why? They lack critical mass even though they may be innovative. Zoho? Nope. ThinkFree? Interesting concept but not enough mass. Meanwhile none of the alternatives are perfect. Browser-based subscription services sometimes lack offline access. Offline suites don't integrate with the Web with anytime, anywhere access or enable seamless upgrades.
If you want to dent the Microsoft Office juggernaut with a Web alternative it's going to take enough users to get businesses to see it as an alternative. That's why Google's Office warrants attention. Google actually has enough users and mass to be a threat (someday) to Microsoft Office. Other alternative office suites may indeed be technically better, but if only 200 people are using them they are irrelevant. And office suites that cater to one faction of the tech world, say Linux fans, won't have enough folks on board to matter.
That's the harsh reality, but it's highly likely that most of the innovation happens with these smaller players. Here are a few worth studying. These five are also mentioned often by readers. Just because they don't have a chance to kill Microsoft doesn't mean we can't learn from them.
KOffice. An office suite often cited by Linux fans. Like other open source programs it could gain momentum if Linux takes emerging markets by storm. For now the jury is still out on the category.
5. WordPerfect: An oldie but a goody, but every once in a while Corel fans predict a return to glory. David Berlind discusses the WordPerfect roadmap, which puts Corel smack in the middle of the office suite scrum. WordPerfect’s biggest advantage: It's half the price of Microsoft Office. Disadvantage: It still costs a lot more than open source alternatives and its in the large shadow of Microsoft Office. Overall the reviews are positive.
Of course, Microsoft isn't standing still and will address the challenges from ankle-biting upstarts and Google with some form of Web-based office suite, more fully integrating online and offline capabilities. Read/WriteWeb has a good analysis of how Microsoft will respond to the online office threat.