Biz Stone and Ev Williams, founders of Blogger and Twitter, have launched two new (invite only while in beta) sites. Both are accessible with a Twitter login. From what I can tell, Medium is primarily a curation/collection technology that uses collective processes (votes, apparently) to bring things to the fore, while Branch allows topic-oriented conversations to develop from Twitter. 

The really interesting thing for me about this, especially given the couple's enormous success so far in designing winning technologies, is how neatly they fit with the taxonomy of social forms that Terry Anderson and I have developed and that, by happy chance, forms the backbone of a book we're writing. There is a huge trend towards topic-oriented sites right now and away from net-oriented sites. This is about sets of people with shared common interests, not social networks. Social networks are (optionally) there in both the new tools and they are not going away any time soon, but the main social form that matters here is not the network, but the fact that a lot of people are interested in the same thing. Branch is particularly interesting as it allows invited people to talk about something: so far, very much like a traditional discussion-oriented group, acting as a neat way to make it easier for topic-oriented groups to form out of looser networks. However, others from beyond that group can follow the conversation, so it acts like the classic goldfish bowl (one of my favourite ways to liven up a classroom-based lecture) but on a grand scale.  

ps...

I've just been playing with Branch - wow. This is good: incredibly neat and smooth transition between sets, nets and groups, delightful interface. One thing that particularly stood out for me (because it confirms my feelings about the thinking behind Twitter and why it is not even close to being like Facebook) is a quote from Ev Williams at the branch http://branch.com/b/the-volatility-of-social-spaces