Yahoo! has publicly launched two new (previously internal) libraries
calibre is a free and open source e-book library management application.
The Freesound Project is a collaborative database of Creative Commons licensed sounds. Freesound focusses only on sound, not songs
jQuery is a Javascript library that takes this motto to heart: Writing Javascript code should be fun. jQuery acheives this goal by taking common, repetitive, tasks, stripping out all the unnecessary markup, and leaving them short, smart and understandable
A Modern, Lightweight Open-Source JavaScript Library for Interactive Maps
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.