A mod for the game Factorio, mirroring the world map north/south and/or east/west.
This mod will ensure that both halves, or all four quarters, of your world map are identical mirror images of each other, for multiplayer/challenge balance.
There are mod settings available to control mirroring on the X and Y axes, and to move the mirror location away from the origin (4 chunks by default).
It will only apply to newly generated chunks, and will produce discontinuities in existing maps.