Writefreely is a pretty calm and clean blogging software. Pretty much a "here's the editor, I'll take care of the rest." type of software. That's nice and pretty much what I was looking for, coming from Hubzilla. It does RSS/Atom and even ActivityPub and comes with a nice and boring default theme that worked for me.
But the newest version doesn't work for me anymore. Accessing the index page results in an internal server error. Maybe it's due to shenanigangs on how I was building and running writefreely, but it broke for me and couldn't be bothered to work on it. I write so few texts, that it basically should just work at any time. Writefreely obviously didn't work for me. Any other active server software might run into similar problems, so my goal was a static site generator.
Writefreely stored MarkDown text in it's database, so that's an easy way to export the data.
Thanks Writefreely, it's good software, I'm just looking for something more basic.
Hello Zola
There are probably more than a hundred static site generators out on the internet, each with their own toolbox and amazing functionality. I had found Zola some years ago and was interested, but never quite got bothered enough to actually put in the work and convert my website. I was mainly bothered by it not having a default theme, but since I decided to give it a try, I followed the instructions and looking at the demo of the theme that I decided to use (after-dark) gave me the hints necessary. Also RSS/Atom is supported.
Zola can use MarkDown as source files, so that's an easy conversion - just add a header to each article with some metadata.
The index page only showed the titles. That can be solved by adding <!-- more --> into the article, where the teaser should stop. Not sure if that's after-dark specific or Zola.
My website only has about 75kB of article text in total. Zola config, theme, etc. brings the total source to about 250kB. Rendered, the site is about 330kB. I don't want to wait minutes or even just seconds to see how it looks like. A nice thing about zola is that it's fast. Those 250kB take about 40ms to render, or in other words, I could render the full website about 25 times each second. That means it takes the browser longer to load the index page and display it on screen, than it takes Zola to create my whole site with 25 articles. Also serving just a static site is probably the fastest and most secure that a webserver can be.
Not sure if I'll really care about categories, but for now all articles are in the same category.