draw.io is pretty good IMHO. The fact that it has a reasonably rich set of built-in shapes, and you can add any arbitrary jpg or png file to your diagram, make

draw.io is pretty good IMHO. The fact that it has a reasonably rich set of built-in shapes, and you can add any arbitrary jpg or png file to your diagram, makes it immensely useful IMHO. I also love that it integrates with Google Drive or you can download/upload an XML file yourself.