(And ARPAnet begat the Internet, which begat the World Wide Web, which begat Web 2.0.)
"For each of these three terminals, I had three different sets of user commands. So if I was talking online with someone at S.D.C. and I wanted to talk to someone I knew at Berkeley or M.I.T. about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. [...] I said, it's obvious what to do (But I don't want to do it): If you have these three terminals, there ought to be one terminal that goes anywhere you want to go where you have interactive computing. That idea is the ARPAnet."
We're in a parallel situation today in online social networks. There are a bunch of them, they don't really interoperate, and it's obvious what to do -- there ought to be one network, yours, that goes with you anywhere you have an online social context.
OpenSocial and Google Friend Connect provide an equivalent of the routers and gateways that connected disparate digital networks in the seventies, creating a network of networks -- the Social Internetwork.