Google playstore now updates it's marketplace app for Android users with a section to download "free app for the week". If you use an Android Device, you will know that some apps on Play Store are not free. They usually costs a lot of money to purchase them. So these Apps will always be added to the section as "Free app of the week" on Google playstore in order for users to download it for free.
To access this newly-added section, you just have to scroll down on the "Apps" page on Google playstore. For now, only one game is available in the section called dubbed Card Wars - Adventure Time.
Though, More games will always be added.