look for Agent on CPAN.
But Personnally, I don't believe in general efficient all-purpose agents.

You'd better give us more details about what your agent is supposed to do for we can give better hints.

(For example for a net agent, the LWP::UserAgent is fine.
For a system-administration agent, you'll probably have to buil it from scratch.
For a security agent, I recall a project (from india?) about cooperative agents...)

"Only Bad Coders Code Badly In Perl" (OBC2BIP)