[cratermoon]

How many of those rely on LaTeX syntax extensions to render equations?

[ogogmad]

The LaTeX formula language is a separate thing from the rest of LaTeX: It's become the standard for formulas. There are some editors that can speed up writing those formulas. Asciidoc also offers an alternative formula language.

[TchoBeer]

I can't speak for most of them because I haven't used them, but I know that TexMacs doesn't use LaTeX under the hood.