If you are looking for an app that can help you relieve mental stress, try Subway Surfers. This app for both Android mobile and iOS devices allows you to run as you overcome obstacles in a train yard. It is very easy to play.
Geometry Dash is an action game with a catchy music theme. You are expected to move through a square-like platform as you overcome the obstacles on the way. Mastering the art of winning requires a lot of practice and focus.