We added P2P capabilities in Flash Player 10 and AIR 1.5. Now you can create applications such as video chat apps, multi-player games, voice over IP. At the core of this new capability is a new protocol called RTMFP (Real-Time Media Flow Protocol). In order to use this protocol, Flash Player endpoints must connect to an RTMFP capable server. This means that before starting to download or upload directly to other clients, the client first needs to establish a connection to a rendezvous service server and this service helps establish the connection with other clients.
Until recently this was the missing piece for all of you who wanted to try the new feature. Now you can use the Adobe Stratus service. Stratus is in beta, so you can find it on labs.adobe.com. You can visit its page here, and FAQ page here. If you want to start playing with it, just go to the Stratus home page. Using your Adobe ID account you can sign up for a developer key. While it is in beta, this service is free.
LATER UPDATE: here you can read an article on Stratus and P2P http://www.adobe.com/devnet/flashplayer/articles/rtmfp_stratus_app.html