Automatic add-on module installs with PLT Scheme, Squeak, etc.
PLT Scheme is a very good (and free!) programming environment: a fairly nice UI for writing and debugging Scheme code with fast execution. Small runtime applications are possible with a little work using the underlying MzScheme native compiler and runtime. Cool stuff. PLT Scheme has modules for web servers, web services, XML processing, etc., etc. Usually I use LispWorks Common Lisp (a fairly expensive, but very well supported and very high quality product) for Lisp work, but the free PLT Scheme is fairly competitive. LispWorks allows the easy generation of small and extremely high performance standalone applications but lacks web services support. PLT Scheme has good web services support but is more of a hassle to make standalone applications.
I used to have to use Perl occasionally for work (yuck!). The only thing that I miss about Perl is the CPAN library and auto-installation facility. Now more reasonable programming languages have this facility also.