Some pretty neat CGI scripts can be found at the CGI Resource Index which you will find in the resources pages. Many of these scripts are totally free for you to use and abuse, however in most cases you will have to pay the extra for something that is totally free of links back to the authors page or free of advertising. Quite understandably so too. First of all let's look at the practicality of installing someone else's script for your own personal gain. Web based software development is an expanding and lucrative market.
Software is the best possible merchandise to sell over the Web.
Write the program, setup a place for it to be downloaded from and sell an encryption key to make it work. Unfortunately for us we don't know, or want to know how to start writing Perl scripts, so this is not going to be a get rich scheme for us. Once a script has been written, if it's good, then the author can make it freely available for use. If you want support, upgrades, manuals etc then you need to pay for the commercial version. The principle is the same as shareware.