Enzyme is an architecture for creating user-searching-user applications. Right now, it is primarily useful as a resume create/search and HR management system. However, it's potential uses are wide-ranging, and it offers PHP developers an alternative to relying on simple "keyword" searching systems.
The OpenCA Project is a collaborative effort to develop a robust, full-featured and Open Source out-of-the-box Certification Authority implementing the most used protocols with full-strength cryptography world-wide. OpenCA is based on many Open-Source Projects. Among the supported software is OpenLDAP, OpenSSL, Apache Project, Apache mod_ssl.
Orac is a GUI tool for Database Administrators written in Perl, Tk, and DBI. It organizes many useful DBA scripts into a nice graphical interface, for collecting statistics on your database, or diagnosing problems. It currently supports Oracle, Sybase, and Informix. Richard Sutherland's DDL::Oracle Perl module has been integrated with the current version for the Oracle side of things, greatly improving the Oracle developer options on the program.
QSD is a *nix daemon for administering game servers (like Quake, Half Life, etc). It uses a flexible plugin architecture for both authentication and for interfacing with the individual game servers. QSD has been designed from the ground up to relieve many problems game server admins deal with from day to day.
GNU EPrints is a solution for sites wanting to set up archives. By default it is configured to be an archive of research publications but can be easily altered. It is scalable and robust; all metadata is stored in UTF-8 rather than ASCII, and all "phrases" the system uses in user interaction are stored in an XML file for easy editing or translating. The system is built around Apache, mod_perl, and MySQL. Submissions are made via the Web and not entered into the main archive until approved by an editor.