EDIT 2020-06-23: the PR is in limbo, and I'm thinking that a gemini-specific SSG would be a better idea. I really only want trivial templating support and autogenerated indices.
Just a quick mention: I've been hacking on Zola lately. Zola is a static site generator written in Rust that IMHO addresses the pain points of Hugo quite well. Previously Zola only supported HTML output.
Last night I got generic output working, with a simple gemini test site used for integration tests. It's probably going to take a bit of polishing before it's merged (if it is). Meanwhile, the PR is here:
https://github.com/getzola/zola/pull/1059
I'll start using Zola for this site soon. EDIT: no I didn't.