I was tasked to make a "Visio-lite" for a project. The biggest issue was it also needed to be web-based. I evaluated 3 software packages and found Syncfusion Essential Diagram to work the best. Quickly I could do a proof of concept dragging and dropping objects onto a canvas and save/load the resulting diagram. I also liked I could assign values to the objects and make them persistent. If you need to added diagram functionality to your web app give this a try.