Presumably in preparation of a celebration for the 5th Anniversary of the App Store, several popular paid apps are free for a limited time! Infinity Blade II is available on several iOS devices, and is typically priced at $6.99.
Along with Infinity Blade 2, some other good deals are:
Badland (iPad+iPhone, Usually $4.99): https://itunes.apple.com/us/app/id535176909
How to Cook Everything (iPad+iPhone, Usually $9.99): https://itunes.apple.com/us/app/how-to-cook-everything/id409936319
Traktor DJ (iPad, Usually $19.99): https://itunes.apple.com/us/app/traktor-dj/id592052832
Tiny Wings HD (iPad, Usually $2.99): https://itunes.apple.com/us/app/tiny-wings-hd/id541517597