[jaster]

For emacs users, there are some modes with similar functionalities (as expected from emacs!): picture-mode and artist-mode

See for example http://xahlee.info/emacs/emacs/emacs_ascii_diagram.html

[jordigh]

Came here to say this. If it's text, Emacs can handle it.

Oh, also, if you want your ASCII diagrams to render into pretty pictures, I found org-mode + ditaa to work quite nicely:

https://www.orgmode.org/worg/org-contrib/babel/languages/ob-...

[everybodyknows]

Another option for rendering (to SVG) is goat:

https://github.com/blampe/goat