Template within your docs, and xlsx files.
A library for templating within your docx and xlsx files (.pptx unplanned). It works by modifying the xml files in place without touching anything unrelated.
It works on browsers and Node.js. See it live on the site.
There is a custom-developed language for working with sheets inspired by functional programming, making it deterministic, robust, and extremely composable. It's also possible to define your own functions, for extra customizability.
Read more about the sheet templating language here.
Check this doc for more info. You can also try it out on the live astro-powered demo here.