Parse, validate, manipulate, and display dates in javascript.

Library of some pretty slick animations using only css3 (no js).

Sentry is an open source PHP 5.3+ fully-featured authentication & authorization system. It also provides additional features such as user groups and security features. It's framework agnostic (composer), so it can be installed on Laravel, CodeIgniter, etc. They recently released their official docs and I really like how the interface works. Related discussion: http://www.reddit.com/r/PHP/comments/1aitay/simple_powerful_and_easy_to_use_authorization_and/

Canvas Query is a wrapper library for HTML5 Canvas element which allows it to be used with jQuery-like syntax. Also it adds a lot of common use image manipulation methods mainly convenient for gamedevelopers.

"Notificon is a javascript class for providing client-side favicon notifications. Instead of requiring a number of favicons be created and served up to the client, you can specify a label and a favicon (default being the current favicon) and it will generate a favicon notification."

"Google Reader is a popular RSS feed reader, and this library allows you to tap into the functionality exposed by their API without having to get your hands too dirty.In addition this library can parse the XML returned from the Google Reader API for you into nicely formatted objects for easier consumption."

"WireIt is an open-source javascript library to create web wirable interfaces for dataflow applications, visual programming languages, graphical modeling, or graph editors."

Matchbox is a modular system, which means you can group your controllers, models and views for a specific section of the site together. There's a new competitor called Modular Separation. Modular Separation is purely PHP 5 which gives it a slight edge over Matchbox from the get-go as it can leave out a lot of the extra PHP 4 support and go right for the much cleaner & quicker full OOP approach. It also includes 404 routing.

Popular CodeIgniter PyroCMS has now been converted to use Modular Separation and it has shaved a few 100ths of a second off here and there. I am not suggestion you drop Matchbox right now, but give it a try if you are starting a new project.

Check out the thread in the CodeIgniter forums here: http://forum.codeigniter.com/printthread.php?tid=31788

"This library is essentially a wrapper for the Facebook PHP API, but also includes everything you need to get Facebook Connect working with in your CodeIgniter libraries."

"A juery plugin for mobile web development on the iPhone, Android, Palm Pre, and other forward-thinking devices."

"jQuery Tools is a collection of the most important user-interface components for today's websites. This single JavaScript file weighs only 5.8 Kb"