Building an application that uses the bit message protocol to allow people to communicated securely. https://bitmessage.org/bitmessage.pdf
It will also incorporated a mail handle such as erlmail to allow user to authenticate their email addresses so that they can be used as usernames and also for inviting new users to download the software. http://code.google.com/p/erlmail/
It will also incorporate a torrent handler like etorrent to allow users to send large file directly to each other using DHT without the need for tracker servers. https://github.com/jlouis/etorrent
This application will run on the users local system and but it will have a web interface talking to a local host. This way the interface will be reusable on multiple OSs.
I have a strong preference for building this app in Erlang.
I complete mockups of user interaction are ready but not included here