BugKick is an open source bug tracking and task management application (source is hosted on GitHub) that is “light” in means of features (which i sometimes nice).
iLightBox is a fresh alternative to other jQuery lightbox plugins and there is a strong chance that, although it is a paid resource,В it may become your favorite.
Textpattern is an open source content management system, built with PHP/MySQL, that offers a flexible usage for designers, publishers/bloggers and end-users.