I just dropped this on Printables: A FreeCAD based custom size box generator. I’ve been using it for all kinds of stuff. Maybe some of you lot will get some use out of it, too.
https://www.printables.com/model/770701-parametric-simple-custom-box-maker-freecad-generat
Plug in your parameters, make a box with filament hinges – No hardware required. No screws, no nuts, no supports, no glue, no Fusion, no proprietary software, no going cross-eyed looking at OpenSCAD code.
(And yes, the default size in the file will make an M:tG card deck case.)
Just because it renders that way doesn’t mean it is. Depending on your zoom level and probably settings, FreeCAD will simplify the rendering on your screen for performance.
If you used the circle tool in a sketch, the final output when you export or whatever will be a circle.