Eskild Hustvedt has written a tool, jesgemini, to convert a number of static site generators to Gemtext.

jesgemini is a minimal static site (capsule) generator for the Gemini Protocol. It's designed to be "compatible" with sites built using other static site generators. Compatible here being a relative term, basically meaning it can slurp up a directory tree of markdown files meant for a web-SSG, and spit out a usable tree of gemtext.

It has an external dependency on lowdown by Kristaps Dzonsons. The code for jesgemini is available at Source Hut: git clone https://git.sr.ht/~zerodogg/jesgemini under the GPLv3.