Question about Perl or PHP script?

I want to have a script programmed that i can sell to people to use and host on their own server (web host). Dont worry what the script is yet... I know there is different web hosting servers like windows NT and unix etc. And i know that (or atleast i think) that certain scripts will only work on certain servers. So what is the most common server out their that people use to host their web sites on? What programming language should i have the script written in so it works on ALL servers? Is it possible to have a simple script written that works on all hosting servers so i can sell it to anyone with any host? ## Deliverables Dont know? ## Platform Dont' know?