What is the deal with the ad's you see for "play this game and make money".

Basically I see these ad's all the time, like, "Oh would you like to earn some extra cash, try Black Solitaire" or something like that. But I have never really looked into them because I assume they work on some sort of "to good to be true" basis.

So what is the deal, and, are there any actual apps or games you can earn money by playing?