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.)
I think you could improve the latch design by making it curved, with a large-diameter circle centered on the hinge. But I tried to sketch this in FreeCAD, and my circles are coming out as jaggy polygons instead of round. How do people get anything done with this software?
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.