Mollom

Weblog Tools Collection reviewed the Mollom plugin for Wordpress maintained by Matthias Vandermaesen. From the review:

Mollom works much like Akismet: comments are sent to a central server which uses intelligent, self-learning algorithms to determine wether or not a comment is spam or not. Spam-classification isn’t a binary process and as a result, common anti-spam services perform bad when handling false positives. Mollom takes care of this. If it can’t clearly classify a comment, it will present the commenter with a secure CAPTCHA test instead of dumping the comment on an ever-increasing moderation queue that needs frequent attention. Mollom is a centralized service which can identify spammers across the network of websites who use Mollom. When a single spam-source is identified on one or more sites, the whole network will be protected against spam from that source