This isn't exactly true - so please forgive me for jumping in and promoting my own project now... :-)
Although the implementation is completely different, PageKite (http://pagekite.org/
) is designed to solve exactly this problem - to let people run publicly visible servers on machines that do not have unfiltered and/or public IP addresses. It's free software (AGPLv3) with the backing of my tiny startup company in Iceland. (After a chat with RMS we are considering whether we should make it an official GNU project as well, but haven't really come to a conclusion yet.)
Instead of attempting to provide strong anonymity like GNUnet, I2P and Tor,
PageKite's goal is to be backwards compatible with today's browsers and
today's servers, letting people use the tools and standards they are
already familiar with. (If people want backwards compatibility and strong anonymity at the same time, it is possible to use Tor and PageKite together, at the cost of performance.)
In my opinion, if you want people to gradually migrate to more privacy friendly alternatives than Facebook and Google, then this backwards compatibility is critical - I can't demand that everyone who wants to visit my photo albums install a GNU VPN client or an IPv6 tunnel; my photo album has to work with the web browser and Internet connection they have already.