SolveSpace is free 2D/3D CAD software, but it makes a great tool for creating vector graphics. It is a very small program, so it loads instantly, and it can export to SVG, the commonly used Scalable Vector Graphics format. What makes it useful over programs like Inkscape or Adobe Illustrator is that you can define geometric constraints for your geometry. You can define parallel lines, a line that is tangent to a curve, a line that is a certain distance from a point, a set of points that are symmetric about a line, etc. This makes it easy to create graphics with exact geometry that scale well.

The one shortcoming is that the SVG export will only export geometry, not fills, and there will also be visual representations of the constraints that are defined. You will have to load the exported SVG into inkscape or illustrator to delete the constraint graphics (they all have the same pink stroke/fill, so select similar should do the trick) and set the fills/strokes/effects.