Facebook's engineers thrive on innovation and experimentation. We're encouraged to work on projects that inspire us and build on new ideas, but not all of these features and improvements wind up launching on the site. In some instances, they're not quite ready for prime time, are a bit esoteric or don't quite fit. Now, for all the products that wouldn't otherwise have the opportunity to see the light of day, we're introducing Facebook Prototypes.

Facebook Prototypes let us share the experimentation going on inside the walls of Facebook with the rest of the world. You'll be able to test any of the products and features we launch as Facebook Prototypes and then provide feedback directly to those of us who built them. To access Prototypes, visit the Application Directory and filter by "Prototypes." From there, you can activate or download any of the Prototypes listed.

For instance, during a recent Hackathon — an all-night coding event that gives us a chance to build projects we just don't have time to pursue during regular hours — I worked on an application called Desktop Notifications, for Mac OS X. The application helps you keep up to date with what's happening on Facebook.

Already, you can see when people take actions on Facebook related to you through the notifications that appear at the bottom right corner of your browser or through email notifications — quickly check out a photo you've been tagged in, a new friend request or read a comment on your status update. Now, you can receive the same notifications even when you're not on Facebook.com or checking email by using Desktop Notifications.

After activating the application, you'll see a Facebook icon next to your computer's clock that will light up with a pop-up alert whenever you receive a new notification. When you click on the notification, you'll be taken directly to the action on Facebook in a new browser window. If you want to just read the notification without going to Facebook, you can dismiss the notification by waving your mouse over it. The application also keeps track of your Facebook messages and gives you an easy way to update your Facebook status.

Other Prototypes include Recent Comments Filter, which allows you to sort your News Feed by items on which your friends have recently commented; Photo Tag Search, which enables you to find photos by the people who are tagged in them; and Enhanced Events Emails, which allows you to add a Facebook Event directly to your personal calendar in Google, Microsoft Outlook and many other calendar products with just one click.