.net c# chat software - your code or open source customized

We have existing client software written in .net/C# and want to ADD chat functionality to it. I'm looking for a developer who has experience with live chatting software and file sharing. I need to see examples of your work either with a custom written app in .net/c# or an open source solution you've customized. The features we are looking to implement are: 1. Live chat 2. File sharing between users 3. Username creation and management 4. Usergroups to manage friends 5. Friends List I require full source code from winning bid. Only developers with a working example will be considered.