Mollom is a spam deterrent and overall content moderation system by Dries Buytaert, the creator of Drupal, and Benjamin Schrauwen. It is similar to Akismet. There is a good post about Mollom by Dries on Drupal.org.

I am trying out the Public Beta. Unfortunately I don’t get many or any comments (hint hint) in order to do some good testing. I have good faith in the mind of Dries and think it will become a good option for content moderation (spam killing). I will keep this updated as I learn more.

Of course there is a Drupal Module for it. There is also a Java Library to interface with the API.