@mcc a lot of people I know are asking these questions!
Once upon a time (mid-2008? Oh, I was so naive) I tried to build an "apache/cgi-bin for building cross-protocol decentralized social tools." At the time that was xmpp, pubsubhubbub, RSS, and indieweb-i-guess. I maintain that it's still possible with the modern set of photos, and probably easier than one would reckon (and probably harder, too). I'm not sure what the modern metaphor would be (so many options!)
oblomov