I use DrawIt plugin in Vim... As much as that looks beautiful, why would you open a GUI window to draw plain text? No need(although of course it doesn't look as slick).

A little one I done with it: https://github.com/salgadobreno/dme/blob/master/README.md

Abusing unicode chars, I've done some pretty interesting mock-ups...

According to AlternativeTo [1] there are two software for Windows with similar features [2][3].

[1] https://alternativeto.net/software/monodraw/?platform=window...

[2] http://www.torchsoft.com/en/aas_information.html

[3] http://www.jave.de/