Last week we stumbled across an impressive new Facebook Desktop Notification app for Mac, which had apparently been developed by a Facebook engineer but wasn’t being officially supported by Facebook (don’t let that deter you from downloading it, as it’s fantastic). At the time, we also noticed some interesting references on the page to something called “Facebook Prototypes“, which we speculated may have been a new project similar to Gmail Labs that would let users customize their Facebook experience using experimental new features. Turns out, we were right: Facebook has just taken the stage at TechCrunch50 and announced Facebook Prototypes — a new section of downloadable applications and on-site features that were developed by Facebook engineers as side projects. You’ll be able to browse the Prototypes here, though it appears they aren’t live for everyone quite yet.

Facebook’s Aditya Agarwal explains that we can expect to see a variety of new apps under Prototypes, including Funny products (like Facebook’s Pirate language), and early versions of features they’re working on. He also said that we may see some features that might not appeal to everyone, but some users might enjoy. Among the prototypes presented were a new Photo Tag search, which allows users to search for photos by the people who are tagged in them. He also showed off a feature that lets you filter your News Feed by only displaying posts that have been commented on by your friends.

The Prototypes feature makes sense for Facebook, which routinely runs hackathons where its developers run wild and develop new projects, some of which are eventually deployed to all users (Facebook Videos was one such project). Facebook Prototypes will give developers a chance to share these projects with anyone who wants them, even if they aren’t quite ready for prime time.