VuFind is a library resource discovery portal designed and developed for libraries by libraries. The goal of VuFind is to enable your users to search and browse through all of your library's resources by replacing the traditional OPAC.
SiteBar is the web's leading bookmark server, featuring muti-user/group access, a simple mode for the single end user, full import/export features, skinnable interface, internationalization. It integrates to sidebars of all major browsers.
Lurker is a mailing list archiver designed for capacity, speed, simplicity, and configurability in that order. Noteworthy features include: google-style searching on all fields, chronology preserving threads, multilingual, and attachment support.
Free web-based bug tracking system written on PHP. Some of the main features are: fully custom templates, advanced filters, LDAP support, email notifications, subscriptions, reminders, flexible permissions management, graphical project metrics, etc.