This is a tool that I needed for designing my own coils and to understand the tradeoffs in choosing coil width, depth, and most importantly, wire gauge. These impact the magnetomotiveforce (you usually want more of that) and the heat (you want less of that) and the the amperage (which you may have to limit to match your circuits other components.)

It is completely fee and online, and completely open-source, implemented completely in javascript using free tools. In addition to being a specific design tool, I feel like the 3D display helped me to finally fully understand the tradeoffs in coil design.

Like all Public Invention projects, it is complete free.