We've been using Keystatic in Buttondown for around six months now: we migrated most of the content on the marketing site (which is backed by Next) from MDX onto Keystatic, and were so happy with the experience that the upcoming rebuild of the docs site will be featuring Keystatic as well.

It's hard to accurately describe why Keystatic, because the market for "semi-static content, but also there are some types, but also there's a CMS, but also there's an API" feels so saturated: Gatsby, Sanity, Storyblok, Butter, Strapi, Contentful, the list grows and becomes more confusing over time. Really, the reason why it felt — feels! – so good to use was because everything felt like roughly the right set of tradeoffs:

• It is very fast. (Even at Buttondown's fairly meager content size, MDX was incredibly slow to compile);
• Getting a typesafe API right out of the box makes it much easier to do content buildout;
• There's a CMS that is good enough that I can feel comfortable pointing a technical writer at it, even if it's not good enough that I feel comfortable pointing anybody at it;
• The process of registering and rendering custom components is easy and ergonomic.

It is still early days for the project, but I think it's the best option out there. Give it a shot.