The name is TeXmacs - but "Notice that TeXmacs is not based on TeX/LaTeX." I wonder why they chose that name.

Neither on emacs and nor it’s a Mac first app. Probably the most misleading app name ever.

It isn't compatible with TeX/LaTeX but it does serve the same purpose (and converters are available). I don't disagree it's a weak name, though. The naming implies some sort of rich LaTeX editor plugin for emacs - I need Mike Meyers to leap out and say "Texmacs is neither LaTeX nor Emacs - discuss."

Perhaps it's like "Javascript", trading on association rather than on substance.

It’s heavily inspired by both TeX and Emacs, hence why it’s named after both of those. As if the author had added the best aspects of the two and then some.