Is a great service, but I'd love to have something I can use locally. A _lot_ of my time diagramming is spent disconnected, transitioning over photos of whiteboards to actual diagrams.

Are you aware of anything that is a local client?

There is years ago asciio, works well on linux environments, some distros have it already packaged, otherwise you can pull it from CPAN.

Looks something like this: http://wiki.cornempire.net/_media/asciiart/diagram1.png

Asciio should be available as a package. For example, in Debian, it can be installed:

    sudo apt-get install asciio

Have you tried artist-mode in emacs?

asciio has layers, which is orders more powerful