A year ago last week, Facebook released the Facebook Platform, enabling users of the social network to create their own applications. Today, 400,000 developers and 24,000 applications later, the company introduced the Facebook Open Platform, which releases much of the Facebook Platform source code to the development community.

The so-called fbOpen is now among several Facebook open source projects. In essence, fbOpen delivers a “snapshot of the infrastructure that runs Facebook Platform,” according to a project Web page. By downloading this snapshot, developers can launch an instance of the platform and test their applications locally, rather than uploading them to a server or sandbox for better performance, stability and control. fbOpen also includes Facebook’s API infrastructure, the FQL parser, the FBML parser, and FBJS, and implementations of the most common methods and tags.

“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’ wrote Facebook’s Ami Vora in a blog post today. Also built into the release, she wrote, are extensibility points that permit developers to add functionality to the platform such as custom tags and API methods. “We’re also hoping you use Facebook Open Platform in ways we’ve never thought of. [J]ust as you showed off your creativity with Facebook Platform, we hope this lets you be creative with the foundation of the platform itself.” All the code is being released under the Common Public Attribution License with the exception of the FBML Parser, which is controlled by the Mozilla Public License.