Stake also allows you to play their games for fun. Before playing slots for example, there is always a pop-up that lets you select if you want to play for fun or use free money. While I’ll admit I’ve never played “just for fun” on Stake, I do really appreciate that it is an option and think it probably isn’t the worst way to pass some time.
Many popular casinos have such demo feature games that players can play for fun without the need to make deposits at first, and that is what most newbies use to learn one or two things about the game before the go-ahead to try it in real money games, you are right about stake having that feature and a few time I was on that casino I make use of the free games to avoid losing money in real bets.
But aside from that I don't think there is any casino that allows you to bet real bet without money and allows you to withdraw the winning in reality because doing so is the same as giving free money which the casino will never do such thing and the highest free money from them is in form of bonuses and nothing more.