SocialStream, an ambitious social networking project aimed to interconnect existing networks, lets you post content to and from social networks.

From the project website:

Socialstream allows users to post content to any participating network. Because of this, it can inherit the ability to handle any type of content: photos, blogs, video, audio, events, and many forms of structured data. By consolidating the controls for publishing in one place, users are free to consider the content of their posts, and only as an afterthought specify the people who should see it and the sites that host it. By consolidating content in one place, Socialstream increases the benefit of commentary and referring posts, and lowers the barriers to participation.

It hasn't launched yet, but with Carnegie Mellon University at the helm and Google lending a helping hand, it could represent the dawn of a new era of social networking.