User Level Networking is software designed to allow the dynamic allocation of IP addresses. The basic idea is to give different IP addresses to different users, thus identifying the UID-HOST pair with an IP address. It includes a patch to the kernel which must be applied to every client in the LAN, a suid executable which will be used by the users to get their IP address from the server and activate it on a virtual interface (like eth0:*) on the local computer, and an executable which will be launched by sshd on the server host.
ebiff is an email notification agent like biff or Xbiff. It is plugin-based, so its capabilities are only related to the plugins already written. Currently, there are plugins to access mailboxes in mbox and maildir format, notify the user by playing a sound, writing an on-X-display message, broadcasting a message to all users' terminals, synthesizing a voice that says what you want, or drawing a gbuffy-like window using GTK 2.
FreePOPs is a POP3 server that is scriptable in LUA. This means that you can tailor it to your needs by writing a plugin. Plugins are currently implemented for using FreePOPs as an RSS aggregator, a POP3 forwarding server, and a POP3 interface to the webmail services of libero.it, inwind.it, iol.it, blu.it, lycos.it, tin.it, virgilio.it, gmail.com, aol, hotmail, fastmail, mail2world, yahoo and many more (see the Web site for an exaustive list).
Sync Mail Dir is a set of utilities to synchronize a pair of mailboxes in Maildir format using SSH to transfer data. It provides the smd-pull utility to pull changes made on the remote mailbox, smd-push to propagate local changes to the remote mailbox, and smd-loop to iterate push and pull in a timely way. Unlike OfflineIMAP It requires no IMAP server to be installed on the remote host. Moreover, it never attempts to automatically resolve conflicts between incompatible mailbox statuses; it just notifies the user explaining how he can fix the problem. Its design is similar to that of Maildirsync, but it is more efficient in terms of CPU cycles and disk I/O.