I'm guessing the parent is being down-voted for simply pasting a link with no context.

For the kind of diagrams I typically want to include in a Markdown document (a quick DB ERD, a class diagram, a deployment diagram, state charts, or sequence diagrams), those things can be described in a simple descriptive form and then drawn from that. I don't want to draw.

I think a good tool for that is Mermaid.JS (see the parent link).

However, what I think the Markdeep approach has over the Mermaid approach is that Markdeep fits the general ethos of Markdown much better: start with a readable doc. I would agree that an ASCII art picture is more readable than Mermaid.JS.

It'd be nice to see approaches like Mermaid with a bit more energy into making the markdown behind the diagrams a bit more readable relative to where they are now, so that consumers of the raw markdown have an easier time.