I find easy_install extremely useful for programming with Python, and the same as rubygem with Ruby.
Does Lisp have similar feature? I understand that there are many Lisp implementations (clisp, sbcl, clozure cl ...), but I just wanted to know what would Lispers do when they need to find and use Lisp library functions.
It's been a tricky problem, and there have been several attempted solutions.
I recently did a survey of Common Lisp users, and most of them simply manage libraries by hand by downloading project archives and checking things out of git, cvs, svn, etc.
The next most popular method of library management is a program called "asdf-install". See http://cliki.net/asdf-install for some info about it.
Some people use a program called clbuild. It grabs libraries from git, cvs, svn for you. http://common-lisp.net/project/clbuild/ has more info.
I'm working on a project called Quicklisp. I'm starting a public beta tomorrow. I think it has some advantages over manual library management, asdf-install, and clbuild, but unfortunately it doesn't have any documentation or information. It does have a group of enthusiastic users, though, and I hope it will help people get the CL libraries they need. For more information, see http://quicklisp.org. The link to download the beta will be there tomorrow.