Sonic Jam
"Sonic Jam" is a compilation which contains the four main "Sonic the Hedgehog" games released on the Sega Genesis: "Sonic the Hedgehog", "Sonic the Hedgehog 2", "Sonic the Hedgehog 3", and "Sonic & Knuckles". Unlike future "Sonic" collections, "Sonic Jam" does not use a Genesis emulator; the games are proper ports, and all are nearly identical to the original Sega Genesis releases, with the exception of minor bug fixes. "Sonic Jam" emulates "Sonic & Knuckles" "lock-on technology"—a special feature that allows the player to merge elements of "Sonic & Knuckles" into previous games, resulting in changes to the level design as well as the choice to play as Knuckles the Echidna in "Sonic the Hedgehog 2" and Tails in "Sonic & Knuckles".
Retro Engine
Christian Whitehead first created the Retro Engine for use with a 2007 fangame entitled "Retro Sonic", which is based upon the original "Sonic" games released for the Sega Genesis. The game became notable after its release for its accuracy to the games, despite not being a ROM hack or modification to an existing "Sonic" game. "Retro Sonic" later merged with two other "Sonic" fangames, "Sonic XG" and "Sonic Nexus", to form "Retro Sonic Nexus".