Today, Facebook just announced that it’ s opening up the Facebook Platform. In their words:

Now we also want to share the benefits of our work by enabling other social sites to use our platform architecture as a model. In fact, we’ll even license the Facebook Platform methods and tags to other platforms.

The announcement in even more interesting in the light of the fact that Bebo, a founding member of Open Social, has apparently been working closely with Facebook in their release of their own “Open Application Platform” (some say it’s virtually a clone of the Facebook Platform). And Bebo’s no small potatoes either, according to comscore among social networks they rank third in North America (by number of users), and are first in Europe.

So what does this mean for Open Social? The InsideFaceBook blog offers a answer from Bebo CEO Michael Birch:

“What about OpenSocial?” Clearly the Facebook Platform is different than Open Social. We attend the Open Social meetings. We’ll start development early next year. We want to give developers the choice to develop on the Facebook Platform or OpenSocial on Bebo.

When Google launched Open Social, their wide array of partners and open approach seemed to catch Facebook by surprise. And yet all that perceived openness was enough to overcome some of the “not quite ready yet” problems and fragmented implementation plans among OpenSocial partners. However, now Facebook offers a way for developers to have their cake and eat it too – with a mature API that they’re willing to share beyond the walls of Facebook. It’s a big win for facebook developers, and helps thwart Google. Dave Winer calls it: “the end of OpenSocial”.

This is a very positive move by Facebook, and with a bit of luck, might signal the beginning of a new more open approach by Facebook in general. It’d be nice for Facebook to elaborate more on their approach to “licensing” to other platforms. And of course as third parties get involved there will also be some “embrace and extend” tensions as those parties pick and choose what gets implemented (something OpenSocial hasn’t been immune to either). As Bebo’s Jessica Alter puts it:

“We’re going to do our best to keep things as compatible as possible for developers. However, it will be an 80/20 thing. We want to do most of the same things with our platforms.”

With Bebo now riding shotgun with Facebook, Google has its work cut out for it if it wants to keep other OpenSocial members from breaking ranks.