AI::Prolog is a predicate logic engine implemented in pure Perl. In predicate logic, instead of telling the computer how to do something, you tell the computer what something is and let it figure out how to do it. Conceptually, this is similar to regular expressions. The AI::Prolog distribution contains a Prolog shell called aiprolog and two short adventure games, spider.pro and sleepy.pro.
Algorithm::Diff is a Perl module for computing the difference between two files, two strings, or any other two lists of things. It uses an intelligent algorithm similar to (or identical to) the one used by the Unix `diff' program. It is guaranteed to find the smallest possible set of differences.
Amethyst started as a port of Infobot to POE, continuing as a generic bot core with the ability to handle multiple connections using different protocols (not necessarily IRC) and soft route the incoming messages through a number of processing centres. One of these processing centres contains much of the original Infobot core.
AnyEvent provides an identical interface to multiple event loops. This allows module authors to utilize an event loop without forcing module users to use the same event loop (as only a single event loop can coexist peacefully at any one time). The interface itself is vaguely similar but not identical to the Event module. On the first call of any method, the module tries to detect the currently loaded event loop by probing for an already-loaded event loop, such as Glib or Event. The first one found is used. If none is found, the module tries to load an event module, and failing that, it will fall back to an optimized pure Perl implementation.
Apache SpamAssassin is an extensible email filter that is used to identify spam. Once identified, the mail can then be optionally tagged as spam for later filtering. It provides a command line tool to perform filtering, a client-server system to filter large volumes of mail, and Mail::SpamAssassin, a set of Perl modules allowing Apache SpamAssassin to be used in a wide variety of email systems.
Apache::Session is a persistence framework whose purpose is to provide session management to Web developers. It is designed to work with Apache and mod_perl, but it does not depend on them and will work with any Web server. This module provides a set of classes that give the developer maximum functionality. Session data can be stored in a database, flat files, or shared memory.