Just adding DatoCMS (https://www.datocms.com/) to the list of CMS specifically designed for static websites (shameless plug)!
Here Netlify is listing all the available products in this niche, both commercial and open-source: https://headlesscms.org/ Things are moving.. slowly :)
Here Netlify is listing all the available products in this niche, both commercial and open-source: https://headlesscms.org/ Things are moving.. slowly :)