Sonic 20th Anniversary is an application in the App Store for iOS devices. It was only released around Sonic's twentieth anniversary then removed from the app store.
Sonic the Sketchhog
Sonic the Sketchhog is a minigame in the application. It is a 2D sidescroller platform game. The game features Sonic in a hand-drawn doodle style defeating Badniks like Crabmeat, as he advances his way though a drawn level.
This game was originally released as Sonic Freehand in Japan during June 2010 for mobile phones with keypads.
Sonic the Hedgehog 4 Demo
There is also a LITE version of Sonic the Hedgehog 4: Episode I that can be played for sixty seconds of trial time.