Shtuff Chat - Free Group / Team chat with persistent history.
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
JabbR - A chat application built with ASP.NET and SignalR.
Softros LAN messenger - LAN messenger for an internal office chat for home or business users. It does not require a server and is very easy to install and use. It supports personal chats, group chats, message brodcasting, files transfer and remote desktop access.
Smarsh Instant Messenger - smarshIM Mobile is a free application download that requires a paid account on the smarshIM service...
MyChat - Secure instant messenger for any network