Facebook: The First Level 2 Platform

A quick follow up to my previous post on platforms. In Marc Andreessen’s article on The three kinds of platforms you meet on the Internet, he writes:

  • In the Internet realm, the first Level 2 platform that I’m aware of is the Facebook platform.

Marc defines a Level 2 platform as a platform that lets “developers build new functions that can be injected, or ‘plug in’, to the core system and its user interface.”

Is Facebook really the first to do this? Does anyone have an example of a company that was doing this before Facebook?