I like ghostwriter. Its a simple KDE app, but i use KDE so it perfectly suits my needs.

Assuming you’re running Linux and don’t need any advanced features, Apostrophe works well. Obsidian is also a great cross-platform option.

I use Obsidian for all of my personal notes on Android and Linux. Syncthing keeps the vault synchronized between the two.

If by GUI you mean WYSIWYG, I don't know of any! Very mysterious to me why this has not been properly taken on given the popularity of markdown.

Once every year or so I check out everything that's available and try out any new or upgraded packages I can find. All have at least one of the following issues:

• Massive bloat, often electron is significant culprit
• Stuck on the 2 column editor concept, generally with only rudimentary markdown implementation
• Fly by night new projects which are quickly abandoned in beta state
• Only want to access files within a certain subdirectory which may or may not be configurable; this is rarely the only problem but it's very common in the PKM-type packages

I never quite got it to work properly but Zettlr suits some people. You might be able to cobble something together in Codium. Both those have the bloat issue. There are some self hosted browser-based editors if you are interested in that sort of project. The best and closest I have found is Joplin but it isn't actually a markdown editor. I wish someone would spin an editor off from its code base; surely the skeleton is there.

I just started using Trilium on my homelab. It's got a lot more than just markdown, but also supports markdown.

Joplin? More of a note taking app in general though.

Also using MarkText & also interested in this.

Ideally I'd like something like a Markdown word processor with toolbar & buttons to do things:

• to tide me over until I learn the shortcuts
• to overcome shortcuts that don't work on my keyboard (MarkText at least offers a GUI way to remap shortcuts. Typora had 80% broken shortcuts & expected me to hack a JSON to fix their shit. And what passed for instructions on that didn't work.)

Geany with Markdown plugin

I use Markor on my phone and Notepad++ on my computer.

I also have Obsidian, which isn't FOSS and is built to save files with every change which I don't like, but has some nice display features. I mostly use that one for viewing Markdown files, and the other two for writing them.

CryptPad is a browser-based office suite like Google Workspace, and one of its document types is rich text, text that can be italics, strikethrough, subscript, ​​​​​​​and stuff.

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|Who knows?|* It's worth experimenting with compatibility* But this is turning into a self-demonstrating comment|
|I'm still trying it myself|It doesn't look bad|

You can export those as Markdown.

This comment was written in CryptPad.

org mode and pandoc :P