Shtuff Chat - Free Group / Team chat with persistent history.
JabbR - A chat application built with ASP.NET and SignalR.
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Smarsh Instant Messenger - smarshIM Mobile is a free application download that requires a paid account on the smarshIM service...
Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.
Chatango - Add free live chat to any web page. Chatango is a live group on your site