A system for filtering messages from your IMAP inbox on-demand. Filters are defined in an XML file. Matching messages can be moved, copied, or deleted. This is all independant of your choice of email client, as long as you use IMAP.
Active Spam Killer for Windows (AfW) is a challenge/response spam filtering system for the Windows platform. Based on ASK for Linux by Marco Paganini, this project adds a POP3 client/server wrapper and web administration, as well as Windows compatibility
Spitman is a spam filter, written in python and intended for desktop use. It will fetch the mail from the mailserver and put this in a local file, wich your mail client can check.