xmpppy is a Python library that is targeted to provide easy scripting with Jabber
Asynchronous Unit Test Framework for haXe
Lightweight GUI framework for haXe targetting Flash 7, Flash 8 & Flash 9
This is A pathfinding library. It has simple API for easy use in games
Raphaël is a small JavaScript library that should simplify your work with vector graphics on the web. In case you want to create your own specific chart or image crop-n-rotate widget, you can simply achieve it with this library.
Here is my short list of the most important open source [free] information retrieval libraries being used today that are undergoing active development as of writing. It is a mixture of engines used for both research and industrial applications.
Mapstraction is a library that provides a common API for various javascript mapping APIs to enable switching from one to another as smoothly as possible.