Don't expect to get much help on this one, but asking anyway.
It appears to be a medieval pfennig from somewhere around Germany; of course, medieval pfennigs are supposed to be silver, while this is obviously copper.
Possibly a contemporary counterfeit? Would be neat if it was!

14 mm (side of square), 0.46 grams.
Probably uniface, but I'm not 100% certain. Pretty far gone one way or another.