Bliz is incredibly easy, interpolated server-side scripting for Gemini. I created Bliz, and it powers this site.
In short, write plain text files as normal, but insert scripts in the middle of them.
Read the documentation to learn more
Introduction to server-side scripting with Bliz, by fedi.flounder.online
Mysidard's tutorial on server-side scripting with Bliz
Roboron's Bliz tutorial (in Spanish)
Android: Lagrange's Android port
Highlighting for Bliz/Gemtext.
If you're not sure how to use this, try saving bliz.el into ~/.emacs.d/, then add the following code snippet somewhere in ~/.emacs:
(load (expand-file-name "~/.emacs.d/bliz.el"))