Apple iTunes has a free iTunes App Sale: The Lost City (normally $1.99).

About

The city before you, deep in the mist shrouded forest, can't be found on any map. It shouldn't even exist. Though it's been asleep for a long time, you feel a mysterious power begin to awaken from the ruins around you.

Requirements

• Requires iOS 5.1 or later
• Compatible with iPhone, iPad, and iPod touch