Sonic 1 is available on IOS using the new retro sonic engine made by christian whitehead. They added tails and knuckles as playable characters, a 7th chaos emerald(and special stage), a whole bunch of items from the beta of sonic one in debug mode, super sonic/tails/knux, time attack, leaderboards, and new areas only reachable by tails or knux. Im p sure they added a lot more but the list is really long.