Here it is, many considered it inevitable after OpenSocial, and Facebook have responded by opening up their own platform. Even though the OpenSocial adopters are sticking with Google for now, I think fbOpen will catch on eventually, at least I find it the easiest platform to develop for.
The fb-open-platform.tar.gz archive contains the tools necessary to implement Facebook Open Platform — including the API, FBML (Facebook Markup Language), FBJS (Facebook JavaScript), and FQL (Facebook Query Language) — in your own environment. It also contains libfbml-1.2.0.tar.gz, which contains the essential libraries for parsing and rendering FBML.