Quantitative Venn diagrams.

Prism offers tools to draw circles and text, and you can use those to create informal Venn diagrams. 

 Some people want to create quantitative Venn diagrams, where the overlap (and perhaps the relative size of the circles) is data-driven. Prism does not create quantitative Venn diagrams.  

This FAQ used to link to a free tool from Google. It has been deprecated but should still work.

This free Windows program creates quantitative Venn diagrams with two circles, and this one handles two or three circles. We haven't used either so are providing only the link, not a recommendation.