TeXmacs is also completely distinct from TeX!
It does use TeX-inspired layout algorithms, with modifications to make them better fit real-time typesetting as you type.
It's also striving to be an environment for interaction with other tools, (not unlike Jupyter Notebook).
If you want a structured scientific web editor with collaboration, check out also https://www.fiduswriter.org/. Built on top of ProseMirror.
But Fidus is closer to "WYSIWYM" like LyX — structured editing with "acceptable" typesetting, and TeX export for high-quality typesetting.
TeXmacs shoots for true "what you get" high-quality typesetting as you edit. Mind you, the edited model is structured in "what you mean" spirit (with quite good UX to "see" the structure), not flat "slap formatting on characters" model typical of WYSIWYG editors.
If you want a structured scientific web editor with collaboration, check out also https://www.fiduswriter.org/. Built on top of ProseMirror.
But Fidus is closer to "WYSIWYM" like LyX — structured editing with "acceptable" typesetting, and TeX export for high-quality typesetting. TeXmacs shoots for true "what you get" high-quality typesetting as you edit. Mind you, the edited model is structured in "what you mean" spirit (with quite good UX to "see" the structure), not flat "slap formatting on characters" model typical of WYSIWYG editors.