I assume you can leave your estate to whoever you choose - you don't have to leave it to family even if you have surviving family.
A guy my wife and I loosely knew many years ago died with no family and left a substantial estate (I don't know exactly but believe it ran to several million dollars) to an educational establishment.
If you die without a will then what happens would depend on where you lived and what nationality you had. I believe in some areas it defaults to the government and in others there are opportunities for people to come forward to stake a claim to it, that would then be heard by a court.