Online casinos which give players a certain amount of time to play the no deposit bonus. The free play casinos will start you out with an amount where you can play any of the casino games within the "free play casino", after the time period is over you can collect winnings above the original amount given. The software will let you know if you have met the requirements and when it is ok to collect your winnings. Most free play casinos do require a small deposit in order to transfer the funds from the "free play casino", to the main casino. From there you can immediately cash in your winnings or continue to play all other casino games including progressives.
List of Free Play Casinos and Current Free Bonus