Polish communist money
Nothing to do with being "communist", that money was "official" till 1995 and could be exchanged till 2000 (as far as I remember) but due to very high inflation in late 80's/early 90's it drastically lost its value hence in 1995 new money came in and 1 PLN was worth 10000 old zł. The old banknotes/coins could be worth something for collectors, especially If they are in very good condition (not seriously damaged) and If you are far away from Poland (in PL there's still a lot of them) where Polish money is a bit "exotic", then just try to sell it on your local e-bay or similar platform, there will be a chance to make a few $ selling it.
BTW I read an interview with a guy that is some kind of globetroter and he said when he's visiting some slums in Latin America or other dangerous places, he is stuffing his pockets with the old ZŁs and keeps the real money well hidden, that way he got already "robbed" quite a few times with morons running away with a couple thousand of old złs thinking they just stole a fortune.