Notepad++. You don’t even have to “save” the file! When I used Windows that is pretty much a requirement and it makes an excellent scratch pad.
To add to the others, I recommend Sublime Text
Heynote is my new goto for this usecase: https://heynote.com/
I will check that out! I have been using Obsidian for a while, with some plugins and minor tweaks to make the interface as plain text as possible, but it isn’t always a good “scratch pad”. I love markdown, but I do miss Notepad++ while on my Mac.
I’m also a heavy Obsidian user, but yes it’s a full featured markdown editor.
Heynote does exactly what you like from notepad++ (persistent buffer, no saving) but instead of tabs you can press ctrl+enter and just start a new note (with line numbers starting over at 1) right below the previous one.
On top of that, hit ctrl+L and you can pick your language and get some nice formatting.
All just as lightweight as notepad/++
