Open Source Exchange Alternatives

Justin Silverton put together a short list of Open Source Exchange Alternatives.  Are there others not listed here? There seem to be more and more players everyday. Some offer just email and calendaring, some offer email and calendaring with documents, some offer project collaboration without email. How is this going to shake out? It’s fine that many of these companies are getting press, Zoho, Zimbra, Google Docs, but how are small businesses being penetrated with these offerings? Are they being penetrated with these offerings? What is the future of Hosted Exchange will all of these new AJAX competitors that are likely to have more features? Lots of questions, would be great to get some input here from the players, I know your reading, I see your traffic….