Plus it includes other goodies heretofore unseen outside the realm of hacking mods, like the option to unlock Tails and Knuckles. His achievements include getting the game to run at 60fps and be displayed in 16:9 by expanding the visible area instead of fudging the aspect ratio. The Sonic game is quite a special case, as it’s actually a much deeper modification of the original game done by Christian Whitehead, a developer who also worked on the port of Sonic CD.
They also have a system to save your progress at any time. All of them, except for Sonic the Hedgehog, are emulators packaged in a small frontend from which you can make small adjustments to the game and controls. Luckily, they only appear in the main menu before you start playing the game itself, meaning at no time do they slow down the gaming experience nor do any awkward ads pop up on the screen at inopportune times. The business model for all of them lies in the integrated banner and video ads.