UPDATED on January 30, 2013.
I play a few games that use an awesome daily reward system called Pocket Change
The way it works is that every day you get 10 Pó points when you open each game that has Pocket Change integrated.
UPDATE: Now you can only get 30 points from opening apps. Instead, there are other ways to earn credits, by doing tasks or "events" in apps. You can get these for beating levels in games, and things like that. There is still a daily limit of about 125 points every 24 hours.
So, here are some games that have tasks to earn extra Pocket Change points.
- Candy Monster
(Also Quadris and Pentas from the same developer)
- Crack Your Screen
- Pocket Change
(you also earn the daily reward for opening the Pocket Change app itself)
Update: My app also has it now:
- Be Happy! Lite
- Be Happy! Pro ($1.99)
For more apps, read through the posts in this thread from around January 2013 and later.
All the points you get go between games, and you can save up points to buy real prizes.
I have gotten several prizes already. One nice thing is that you can get Amazon MP3s and eBooks, and then exchange them for Amazon Gift Card credit to your Amazon account.