It sounds like https://astro.build might be a good fit if you're looking to generate mostly HTML and only use JS for a few interactive components on the page. It's still very new and I haven't worked with it yet.
Thanks for the kind words. Unfortunately we have no plans for a self-hosted version. We understand that this is a no go for certain companies and types of information.
Thanks for the information! We did not notice any anomality and are receiving signups, but are looking into what might have caused the issue. In case it's a persistent issue for you, it would be awesome if you could contact us via email so we can further investigate the issue.
If you want something similar to Dropbox Paper, but better optimized towards long-term documentation, you should give Nuclino (https://www.nuclino.com) a try. In terms of organization capabilities it is similar to Confluence. But I'm the CTO so I'm obviously biased.