HTML::Mason is a full-featured web site development and delivery system. Mason allows web pages and sites to be constructed from shared, reusable building blocks called components. Components contain a mix of Perl and HTML, and can call each other and pass values back and forth like subroutines. Components increase modularity and eliminate repetitive work. HTML::Mason is most powerful when used in conjunction with mod_perl, but can be used in standalone applications as well.
WebTools is "system" of multiple modules and libraries. Along with template engine capabilities, it features session management, global variables support, cookies support, and various database interfaces. It also features a pure Perl mail client, categories management, form checking, and libraries such as a CGI-based downloading library, HTML parsers, and a library that makes PHP functions available to Perl for ease of development.
Catalyst is a Web application framework for Perl. It is based on Maypole, and adds many features from Ruby on Rails, Struts, Spring, and Tomcat. The development philosophy focuses on Don't Repeat Yourself, Lego-like components, Code Generation, and very strong testability. It supports a number of plugins, models, views, and controllers.