Dave Winer says in What's missing in our social networks?:
Meanwhile, as we all settle in on these networks, we're also settling -- missing features that would have been developed long ago if we were using open and competitive platforms. At some point the dam will break and there will be a flood of new ideas, or possibly a platform for trying out new social networking ideas.
This made me reflect on all of the attempts that are being made to create a decentralized social network. Some that come to mind are Status.net, Pump.io, Tent and Diaspora. There have also been attempts at protocols like OStatus and Activity Streams.
What exactly do we want?
This is a hard nut to crack because everybody has a different priority of what a social network is. Although there are similarities between Twitter, Facebook and Google+ they all approach the problem differently. Is a news aggregator a social network? My river looks an awful lot like twitter and my blog is available via RSS. I don't hear anybody really talking about this setup being a social network. Although isn't this pretty much what Tumblr is?
Do you have to have private messaging to be a social network? Do you need to have access levels so you can share semi-private information with your followers?
What do I think?
I think the fundamental feature of a social network is the frictionless acquisition of an audience. You need to see a list of people that are following you and you need to easily follow other people. Even though on day one you may not have any followers on Twitter or Facebook, it's very low friction to accumulate followers. Your messages may never actually appear in front of your followers, but there is the perception that people are viewing your content.
Disappointing conclusion
All of the features of a social network are already available in the open web. I can publish a blog with an RSS feed, my friends can subscribe. All the pieces can be replaced. My blog is WordPress, my aggregator has been Thunderbird, Google Reader and now River3. If I want to publish content that's different then what RSS handles I can use something else. The only thing that's missing is the acquisition of an audience which is hard.