A free Venn diagram maker that needs no installation and runs entirely in your browser. Write the sets and their members with indentation and you get a diagram of two or three sets. A set expression such as A|B shades exactly the region you mean, and the outer frame stands for the universe, so complements are visible too. Overlap, radii, colours, and text sizes are all set from the panels, and the finished diagram saves straight to PNG.
The input has four kinds of line. A line that starts with A and a space declares a set, and the rest becomes the heading of its ellipse; sets are declared in the order A, B, C, up to three. A line of nothing but letters is a region header: AB means the region that belongs to A and B but not to C. Anything that belongs to no set goes under -. Indented lines are the items of the region named above them.
A line beginning with * shades the region of a set expression. You can use intersection (AB or A&B), union (A|B), complement (!A), difference (A\B), and parentheses. A region header reads the sets you did not write as "does not belong", while an expression reads them as "either way": with three sets AB means one cell and A&B means two. Because the frame is the universe, !A also shades the area outside the ellipses.
The drawing area is a canvas: zoom with the wheel and drag to move it. Save as PNG writes exactly the framed area at the size you set. Double-click a panel title to switch how the panels are laid out: in the movable layout you drag them wherever you like and keep several open at once, and in the fixed layout a single panel sits in the top right.