Please refer following links:
This is a chat room application. It can run on LAN or Internet. When user logs in to that server, then he/she will be automatically logged in a default chat room. Every one can chat:
Global Text Chat Room Application using C#.NET Remoting Technology[
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This is a LAN chat application with TCP/IP socket programming technology in C#. This application is a multi thread network application and works in a non-blocking way:
TCP/IP Chat Application Using C#[
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This chat application created in DotNet using web services, Have a look just for reference:
Chat Application using Web services in C#[
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