A user interface for non technical users. Which is a real shame because a static CMS is conceptually simpler than a dynamic one, yet WordPress in still the king in this space. Current SSGs are missing out on an untapped niche by burying all their features behind developer-oriented config files and flags when they could be rolled into a nice front-end UI that any non technical user could use. Publii seems to be a promising attempt in that regard.

Netlify CMS is nice, and despite the name it works completely independenly of using Netlify as the host: https://www.netlifycms.org/docs/intro/ I won't lie though it is very akward to setup and use if you aren't using Netlify--documentation is extremely thin, and it's a beta phase feature to selfhost. But it is a really nice and simple editor view that non-technical people could use. This is where the (very thin) documentation for self hosting it outside Netlify starts: https://www.netlifycms.org/docs/beta-features/#working-with-...

Another good one is Jekyll Admin: https://github.com/jekyll/jekyll-admin It's not as nice as wordpress but gets the job done for a basic markdown focused site. Selfhosting it is a lot easier and more documented than Netlify CMS.

Well, it does require making a good desktop editor which isn't something many developers are interested into these days. Publii is a desktop application but even that is an Electron app (which doesn't even take advantage of it being an Electron app and having an entire browser engine underneath and requires you to open the generated site in your browser instead).

www.cloudcannon.com

Integration with design/mockup tools.

This goes some way to addressing that, but it's a proprietary tool for theme tweaking rather than something like Figma, but for production templates

You may be interested in www.plasmic.app, which is a web design tool/page builder that targets SSGs and imports from Figma. (I work on this.)

Stackbit Studio is the closest thing to that I've seen so far.