The weaker the math, the more elaborate the graphics need to be.
There are a lot of interesting programs to create diagrams or graphs. I tried out the trail version of OmniGraffle and it was a joy to work with. But also, quite expensive. A posting in the German Tool Blog and a comment there led me to yEd. Despite its rather unfortunate name, it looks impressive. And it works on Windows and Mac and it’s free.
I’m definitely going to try it out a bit further. And while I am not a fan of Java programs, it does look like a really useful tool.