Centsports is a betting website. They give you one cent to start with and you can use it to gamble on US football, baseball, hockey or UK soccer games. You can bet any amount that you have in your account - a minimum or one cent. If you win your first bet you are likely to amost double your cent. If you lose, they will give you another cent to bet with. This continues until you reach $20 when you can draw out your winnings or continue.
Using this site has taught me a lot of things about doubling:
I would recommend taking a look at Centsports and seeing what you can learn about doubling and gambling.