Abstract Horizon is set of open source projects.

is a little desktop program that allows comparison and synchronisation of two folders and their sub-trees of files.

is a simple HTTP server that can operate without having to conform to the J2EE standard.

Extend is a simple, highly configurable and light-weight application container based on Spring Framework.

Mercury is set of e-mail related projects. It currently has implementations of SMTP inbound server and IMAP 4rev1 server. Both are working based on Maildir JavaMail implementation.

Here you can find some interesting stuff.