Subscript is a very simple stack-based scripting language. The name is short for "Substitution Script" since I made it specifically for that purpose. Given a template page, and several content pages, where a phrase such as "%CONTENT_GOES_HERE%" in the template, I wanted to be able to run a single script that would take the template page, replace that phrase with each of the content pages, and save the results. Essentially, I only wanted to automate the process of copying and pasting so that I did not have to do it by hand.
Subscript is not a particularly powerful or versatile language, even specifically for the tasks I had in mind when I designed it. Regardless, the code for it is not very complicated, and implementing it was fun and taught me a lot of things. And for what it's worth, it does actually work as documented.