Anti-Spam SMTP Proxy Server implements multiple spam filters
Fast Bayesian spam filter along lines suggested by Paul Graham
IGSuite is a web-ajax-based Integrated Groupware Suite
Mailing List Manager - Web-based, Self-Hosted, Feature-Rich
Anti Spam SMTP Gateway
Script set to archive emails at groupwise server side
Zentyal is a Linux Small Business Server
Open Source Anti-Spam and Anti-Virus Gateway
Virtual Appliance of RadicalSpam