LAN messenger, implementing IP Messenger protocol. Its aim was to implement few server-less protocols, but ended with only one.
IP Messenger's alternative
IPMsg is a server-less instant messenger for communication within LAN networks. I used it at some time, but was so annoyed with its UI (which didn't changed since its release for Windows 3.11), so I decided to implement my own version as my Bachelor's project. It was intended as a multi protocol instant messenger, focused on server-less protocols, but ended with only this one.
Unfortunately, I wasn't involved in Pidgin's development at that time, so I was afraid of writting a protocol plugin for it. Now, I'm sure it was a big mistake. Even than, I still say it's one of the better clients for this protocol.