Freebitco.in is a Bitcoin gambling / betting website.
Today it has 12,888,952 registered users that have won up till now 136,366.66352237 BTC playing 64,249,486,313 games.
Wagering is straightforward: you can simply click on a button and wait for the result of a roll to get your free bitcoins, or you can multiply the coins you've earned betting (and you can choose between auto bet or manual bet).
There's a weekly lottery (1.12179504 BTC for the first price) in wich you can participate buying tickets; you also earn free tickets every time you roll your "dices" on the homepage.
You also get free reward points every time you roll: you can redeem them for electronic gadgets (iPhone 7 plus, Apple iPhone 6s, Samsung Galaxy S7 edge, Samsung Galaxy S6 edge, GoPro Hero, Samsung Gear VR, FitBit and so on), for other gifts or bonuses.
There is even a referral program that can make you earn points, Bitcoins and free lottery tickets.
Lastly, you can mine Bitcoins in your browser, simply leaving the tab open and you'll be rewarded accordingly.
It's a simple website with a lot of possibilities to make you earn some Bitcoins and, if you're lucky enough, maybe a large sum of money.