proselint VS novelWriter

You can try proselint, which also has built-in support in null-ls. Its LaTeX support isn't perfect, but it's workable.

Something like grammar-guard, proselint and/or language-tool?

Yep, though there's not a lot to see! Follow the instructions for installing proselint at https://github.com/amperser/proselint and configure as follows:

Vale uses a customizable grammar checker, and you can download some open-source configurations to start working with from the link above. Then, you just need to add something like below to your Emacs configuration: (flycheck-define-checker vale "A prose linter" :command ("vale" "--output" "line" source) :standard-input nil :error-patterns ((error line-start (file-name) ":" line ":" column ":" (id (one-or-more (not (any ":")))) ":" (message) line-end)) :modes (markdown-mode org-mode text-mode) ) (add-to-list 'flycheck-checkers 'vale 'append) (setq flycheck-vale-executable "/usr/local/bin/vale") It looks like you can do something similar with Proselint, which looks wonderful and I have been meaning to try using in my day-to-day: https://unconj.ca/blog/linting-prose-in-emacs.html .

proselint

Full list here. Since the tool is a linter, it sounds like it should work with language servers. I use CoC.nvim for LSP features. Thankfully some smart guys have figured out how to make proselint work with coc.nvim & coc-diagnostic (see here). Now it works for my blog posts just like clangd does for my C++ code.

Proselint is not a VIM plugin. It is a separate tool described as a linter of English prose. Here are some of its features:

You're looking for proselint. https://github.com/amperser/proselint

Novelwriter almost hits the sweet spot, but misses some features and is written in python, which makes some features hard to implement due to the nature of the programming language.

Alternatively, if you want Scrivener-like and are happy with open source projects, novelWriter scratches some of the same itch and is (a) free and (b) available on Linux, Windows, and macOS: it has a similar project-oriented interface to Scrivener, can export projects in HTML, Open Document, Markdown, Plain Text, or PDF, supports tagging and metadata, and uses Markdown for authoring. It's much less hot on importing foreign files (it's really an authoring tool) but is implemented in Python, uses XML/Json for internal files/metadata/configuration, and in use feels like an early version of Scrivener 1.x (which is really what your students want, but Lit'n'Latte discontinued it about a decade ago and you can no longer buy it).

Have you looked at yWriter, Skribisto, novelWriter, or Wavemaker?

novelWriter is an option for specialized "novel" work.

There is Novelwriter, ostorybook (make sure you select the right java during install or it won't run. I used the plain 'JRE' and it worked) and also one called Manuskript.

Yeah, I actually found the AppImage after posting that comment. That goes a long way. novelWriter also looks excellent, but it's still very much not even in the same class.

https://novelwriter.io/ is another option, plus it is FOSS

I've seen one interesting tool that tries to bridge the gap somewhat for writing books, and it does that by being its own software with a split-panel view built-in and bolting extra syntax on top of markdown: https://github.com/vkbo/novelWriter

I haven't used it, but I have https://novelwriter.io/ bookmarked as a FOSS option, especially as it has markdown-like syntax.