Is there something like a spreadsheet application, or simple database, where each cell's content is Markdown, and when I'm editing a cell, I'm doing it in a Markdown editor?
It does not need to be a table. I Just need to have some kind of records (like rows in a spreadsheet), and fields (or cells in a spreadsheet), and each field's content is Markdown.
I do not need a full spreadsheet application like Excel or Google Sheets.
https://notion.so is pretty close to what I need. Everything is Markdown, and you have tables. However, tables are the only things in Notion that are not Markdown, and afaik you can't put Markdown in a Notion table cell's contents.