Berty is a secure peer-to-peer messaging app
You can message and share files inside your intranet without a server.
UFONet - Denial of Service Toolkit
A small, reliable, local network messenger that doesn't need internet
A P2P Messenger which uses JXTA. It provides secure RSA/AES end-to-end
An intranet chat application that does not require a server.
Chat inside a LAN (subnet).