agsXMPP is an SDK/library for the X tensible Messaging and Processing Protocol (XMPP) written in managed C# dedicated to .NET and Mono. 

Our SDK can be used to create XMPP client , server , and components .

Here's a small sample of how easy it is to log in to an XMPP server and send a simple chat-message to another user in only 3 lines of code with agsXMPP:
    
XmppClientConnection xmpp = new XmppClientConnection("jabber.org");
xmpp.Open("myusername", "mysecret");
xmpp.OnLogin += delegate(object o) { xmpp.Send(new Message("test@jabber.org", MessageType.chat, "Hello, how are you?")); };