SAGE 4

Retro Sonic was a fan game project by Christian "The Taxman" Whitehead which would, later on, become the Retro Engine.

ShenSonic is a fan game made by SimSonic, whose real name is Simon Elo, of Magitek Soft which has also created the Sonic in Mobius games. This fan game was previously created using The Games Factory but the final version used Multimedia Fusion Express. ShenSonic is Shenmue but with Sonic characters and makes changes to the plot to fit the Sonic universe. It features 100+ characters, 4 locations, 8 mini-games, day and night cycle, QTE's, inventory system, and much more.

Sonic Robo Blast 2, abbreviated as SRB2, is a fan game for Windows and DOS platforms. It is a 3D platformer developed by a group called Sonic Team Junior, using a modified version of the Doom Legacy source port of Doom, to allow for such things as optional analog control and true room-over-room (something not possible in the standard Doom engine), as well as the standard gameplay elements Sonic games are known for. It has been in the works since 1998 and is currently nearing completion, though several parts of the game are still missing. Sonic Robo Blast 2 is closely inspired by the original 2D Sonic games for the Genesis and attempts to recreate a game with this style in 3D, though it also borrows elements from the current Sonic games, such as Sonic's signature Air Spin Attack. Entirely original to SRB2 is its Multiplayer mode, a variation of classic first-person shooter games with Sonic elements. Due to being built with a modified Doom Legacy engine, the game is also very easily customizable. Custom levels, characters and even source code modifications can be created with the help of external editors.

Sonic The Hedgehog: Time Attacked is a 2003 fan game made by Jamie Bailey. Time Attacked has been compared to commercial games released by Sega because of the game's detailed original graphics and the author's vast knowledge of Clickteam based programming. Dr. Eggman has invented a time machine and uses it to go back in time to defeat Sonic following a failed attempt. Eggman succeeds and begins to create a paradox, causing the present-time Sonic to fade. Once he realizes what's going on with him, he sets off to stop Eggman before he completes the paradox and changes made in time are permanent.