Ask HN: Which hand written diagram software do you use?

I'm currently trying to make graphical explanations on how a software works and would like to make it look good. 6-8 months ago, I discovered an online app that was making it easy to create diagrams with a "hand written feel". However, I can't find it anymore.

Is anyone here using that kind of software? If not hand-written, what tool do you use to create graphical explanations, if any?