I am surprised nobody here mentioned TeXmacs. It's nothing to do with TeX or Emacs, but it's inspired by them. Basically the concept is structural graph based document editing software similar to Tioga/Cedar by Xerox back in 1980s but unfortunately the research and improvement for better tools for editing document seems to stagnate a lot after 90s. I think the idea of having an easy to use WYSIWYG editor for scientific document editing need to be popular now to significantly increase scientist productivity. Remember that web was invented to increase scientist productivity and the rest is history.

On a related note, personally I think Overleaf or Google Docs is missing the point or the pain points. Even though both of them enabled offline editing but they are really a cloud first applications. The better approach is to have something like TeXmacs (native desktop first application) and make a seamless integration with synchronization and versioning to the cloud. With a proper use of synchronization and versioning technology like rsync and Git, together with seamless connectivity tools and protocols for examples Wireguard VPN, WebDAV or even the latest SMB over QUIC approach, I really think this is very feasible. The CONCEPT is similar to the useful and successful Watcom product or now SQL Anywhere database editing application.