Yes you have to install Ruby on Windows but then can use it for your projects. My understanding is the Windows Ruby installer streamlines this for you.
Ruby comes standard on mac but it is locked to an old version. Typically you’d use a package manager on mac or linux to install Ruby
Regarding Jekyll versus other tools - I do like the simplicity of Jekyll. You write content in markdown with some CSS and HTML and some JS if you need it and you can add plugins and themes.
Here is my basic Jekyll site.
A really minimal project has a config (optional actually but it sets your theme) and an index.md file (well actually optional if you use fallback to README.md). So yeah in GitHub Pages the leanest site you can make with Jekyll is exactly README.md and nothing else and dependencies and managed by the system.
Local development of course needs more set up.
Here is a project with an index and config
One for GH Actions using Jekyll 4
The other static generators out have a lot more boilerplate code, I feel like. And written in JS instead of md, so not friendly for non-devs who just want to write markdown and YAML.
There was a recent post here about Bridgetown as an offshoot of Jekyll also Ruby based and intended to be maintained and handle the modern web.
But it lacks the simplicity of Jekyll. From my research, Bridgetown needs Yarn and Webpack to run - which is overkill for the majority of my Jekyll sites which are fine as they are.
That Bridgetown post talks about Jekyll being down to one maintainer, which was news to me. I guess plenty of people use Jekyll but only a few are Ruby developers and so can’t easily maintain it. I have been working with Jekyll for a few years and have some Ruby experience and scratch my head when it comes to most of the Ruby related questions in this forum.
I would check out this post comparing WP, Wix and Jamstack
And check the Jamstack site itself. There are a bewildering amount of options in various languages.
Maybe this will help too
Gatsby has been a the popular choice I think in JS but I heard it is over engineered.
Next.js is similar in also being React-based. Actually the boilerplate seems low. But… your index page is written in JSX and not markdown.
If you use Hugo, you can download a binary and even add it in version control, so there are no Ruby or Go or JS dependencies. Hugo claims to be the fastest.