CPAN, the Comprehensive Perl Archive Network, is one of the strongest and most active repositories for open-source libraries around. These libraries, many of which are packaged as Perl objects, do everything from communicate with Amazon's various Web services (including EC2 and S3), to verify credit cards, to manipulate images, to parse XML, to implement SSL. Because of the somewhat chaotic nature of CPAN, many of these functions are implemented in multiple modules. So there are several dozen modules for parsing XML and another few dozen templating systems, for starters.
