Apps Game Forumla #1

After playing some of the FREE iPad games, i found that they share some similarities.

• list of mission
• create item and wait for production
• level up by gain XP, and unlock some items
• virtual currency to purchase item
• social networking
• special currency/point

How can they make profit? Besides displaying Ads banner, you could purchase those special currencies/points to fasten your production process (that means you are not required to wait for the actual production time)