Bugzilla is the leading open-source/free software bug tracking system, with high-profile installations at mozilla.org, GNOME, Red Hat, and NASA, among others. It features a comprehensive set of fields, attachment management, inter-bug dependencies, email notification of changes, a powerful query interface, reporting, and Web, XML, email, and console interfaces. It can be managed entirely using a Web-based UI. The user UI is customizable using templates.
PerLDAP is a set of modules written in Perl and C that allow developers to leverage their existing Perl knowledge to easily access and manage LDAP-enabled directories. PerLDAP makes it very easy to search, add, delete, and modify directory entries. For example, Perl developers can easily build web applications to access information stored in a directory or create directory sync tools between directories and other services. PerLDAP is OpenSource, part of the Mozilla project.
Sablotron is an XML toolkit which implements XSLT, DOM, and XPath. Sablotron is written in C++, and it can be used from C, Perl, Python, PHP, ObjectPascal, and via a command line interface. It supports the XSLT 1.0, XPath 1.0, and DOM Level 2 W3C specifications. It is designed to be as compact and portable as possible, and is maintained as an Open Source project by Ginger Alliance.
SMTP::Server is a complete RFC 821 compliant mail server, written entirely in Perl. It's extremely extensible, and can easily be adapted to do things like SPAM/RBL filtering, and it's portable to all major platforms, including Win32. The SMTP::Server architecture was written to be very flexible, and its true power comes from the ability to extend/customize its functionality with plugin modules, or Perl code.