I'm guessing graphviz (just because it's popular), but the layout algorithm could have been better. The structure of the two big components is difficult to take

I'm guessing graphviz (just because it's popular), but the layout algorithm could have been better. The structure of the two big components is difficult to take in at a glance. It's a hard problem, sure, but the simple circo algorithm really only works for trees and highly-connected graphs with components, and even then is a little misleading.