Grouper
This week .NET Rocks was among other things about Grouper.
'Grouper is a new Windows based application that allows users to share their personal media within private groups. Grouper uses P2P technology connecting you directly to your friends hard drives where you can share large files in a safe, encrypted environment.'
The program is developed in .NET ! Only the incredible nice looking user interface is worth enough to have a look at it.
Would be really nice when Grouper supported the Jabber protocol.