Indeed, it's difficult to easily imagine a platform that requires enough complexity to facilitate a relatively free market ecosystem where third-parties voluntarily integrate in reciprocal relationship; it's not straight-forward, not obvious, perhaps will be obvious in hindsight once the working model is clearly defined.

Re: "FB wasn't first-to-market"

What platform then first connected close peer groups via requiring a university/college email address for login, for the platform to then quickly associated those users with each other relevancy wise - leading to the network effects that quickly launched Facebook?

(Zuckerberg knowing that there only needed to be one such platform, why he lied to/misled the ConnectU twins who were actively paying him to develop ConnectU - to which he launched TheFacebook first to get an advantage)

Long before Facebook, even before MySpace became huge our small national social network (actually a SMS and logo site that exploded) allowed you to choose a school and show you other people from that school that you could filter by age. Everyone below 20 was using it.

More or less the same thing

Examples of multiprotocol applications are seamonkey, pidgin, miranda, but they use open protocols and purely clients.