As speculated and confirmed last week, Facebook today is announcing that it is open sourcing significant parts of the Facebook Platform code in order to allow developers to get a deeper sense of how the Platform works and invent possible extensions as well. According to Facebook,

The goal of this release is to help you as developers better understand Facebook Platform as a whole and more easily build applications, whether it’s by running your own test servers, building tools, or optimizing your applications on this technology.  We’ve built in extensibility points, so you can add functionality to Facebook Open Platform like your own tags and API methods.  We’re also hoping you use Facebook Open Platform in ways we’ve never thought of – just as you showed off your creativity with Facebook Platform, we hope this lets you be creative with the foundation of the platform itself.

You can download the source to the Facebook Platform here. The zip includes the API infrastructure, the FQL and FBML parsers, FBJS, and implementations of many methods and tags. Most of the Platform is available under the Common Public Attribution License, and the FBML parser is licensed under the Mozilla Public License.

Do you plan on running any part of the Platform locally?