You mean like vim, emacs, nano, kate, notepad, notepad++, wordpad, or any other plain text editor?

Really - I don't get this impulse at all. From my perspective, the entire point of markdown (and RST I assume, though I haven't used it) is that you can easily read and write it using any plain text editor.

If you are going to need a specialized editor to write it, you might as well use html, docbook, docx, odt, troff, rtf, or any of the zillion other formats.