Spamato is a spam filter system that combines several anti-spam techniques, from which thousands of users benefit. It is available as an add-on for Thunderbird and Outlook, and as a stand-alone proxy for other email clients. IMAP and POP are supported.
The project is no longer developed. Last version, 0.99.9, released in August 2007, can be still downloaded from SourceForge.
The SpamBayes project is working on developing a statistical (commonly, although a little inaccurately, referred to as Bayesian) anti-spam filter, initially based on the work of Paul Graham. The major difference between this and other, similar projects is the emphasis on testing...This app doesn't have any features at the moment.