STUN[1] does a very similar thing, including some trickery to get through all kinds of plastic boxes messing with your packets.

AeroFS[2] is another, interesting approach. It's basically a dropbox clone where all data remains on the user's computer. Transfers are encrypted with TLS and tunneled through the company's servers.

Another interesting thing might be Opera Unite[3]. It's an in-browser web server that can be souped up using various extensions like photo sharing, games or chat. As far as I know its NAT traversal is somewhat limited, though.

[1] http://en.wikipedia.org/wiki/Session_Traversal_Utilities_for... [2] https://aerofs.com/ [3] http://unite.opera.com/applications/