- OStatus and pump.io both use ActivityStreams objects to describe actions. pump.io the software uses pump.io the protocol. - Zot, or Zot2, or whatever one would like to call it, is what became the protocol for Hubzilla. - OpenMicroBlogging, the direct predecessor of OStatus, used XMPP. I haven't seen a rationale for why Evan left it. I'm guessing the wish to be more webby, and the fact that PubSubHubBub seemed to be the Next Big Thing in disintermediation and real time search. BuddyCloud uses XMPP to this day, as does Movim. - For concrete info on what the Matrix is (one can be told what the Matrix is!), check out my HPR episode http://hackerpublicradio.org/eps.php?id=2169 .
@strypey The commit for "OpenMicroBlogging 0.9" is from the end of 2010, but I think OStatus actually happened maybe as early as the end of 2009, it was just that nobody wrote it down as a specification, it was just the laconica implementation.