Glib, POE, IO::Async, Event... CPAN offers event models by the dozen nowadays. So what is different about AnyEvent?

Executive Summary: AnyEvent is compatible, AnyEvent is free of policy and AnyEvent is small and efficient.

First and foremost, AnyEvent is not an event model itself, it only interfaces
to whatever event model the main program happens to use, in a pragmatic way.
For event models and certain classes of immortals alike, the statement "there
can only be one" is a bitter reality: In general, only one event loop can be
active at the same time in a process. AnyEvent cannot change this, but it can
hide the differences between those event loops.