gavamail is a POP3/IMAP server implemented in JAVA for reading your gmail e-mail with your favorite mail client. Currently only POP3 is implemented but I hope to implement IMAP too. Libraries provided by the g4j and libgmail projects are used.
IMAP4 server working on top of SQL database (currently PostgreSQL but Oracle may work too). It has some unique features like elimination of duplicate messages throughout the whole system, possibility of clustering or load balancing etc.