The problem with your request for free software is the images of actual fabric, but there are some free websites that help with design.
I have my web quilter bookmarked
https://mywebquilter.com/
And I actually use the graph papers and specific quilting grids here quite often.
https://www.incompetech.com/graphpaper/
But just "free quilting software" or "free quilting app" will start leading you into many different directions depending on what you want to do.
edit: Just realized this might help you out, my usual shopping site equilter, has a design board where you can play some with the fabrics you are buying. So it would be limited to their stock.
https://www.equilter.com/store/st_orderdesignboard