I made https://poemd.dev/ as an online markdown scratchpad that supports GitHub Flavoured Markdown and stores all data in the URL. This means there are no accounts to work with and everything is basically stored in bookmarks if you choose to.

The persistence model makes documents somewhat sharable, but I do find Open Graph previews to be mixed. In Messenger it renders the whole URL, which is quite long due to encoding, and that kills the conversation view.