Anyways. CPAN _is_ the killer app. It's a HUGE, extremely easy to install module/library archive. Perl's modules aren't spread around everywhere but neatly and nicely collected there and you just do a "cpan Foobar" and get Foobar with all possible dependencies included.
Sounds like Ruby's Gems: http://rubygems.org/ or even python's PyPi: http://pypi.python.org/pypi ...