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.
Ni!Mail is a webmail connecting to an IMAP server and using python/nevow/twisted to provide a clean and fast interface. It uses nevow livepage, a library that uses XMLHTTPRequest, to make it very dynamic.