Check out Sonic Robo Blast 2, a 3D open-source Sonic the Hedgehog fangame built from Doom

A reader recently let us know of Sonic Robo Blast 2, a 3D free and open source sonic game built from the open source Doom Legacy game engine.

SRB2 is closely inspired by the original Sonic games from the Sega Genesis, and attempts to recreate the design in 3D. While SRB2 isn't fully completed, it already features tons of levels, enemies, speed, and quite a lot of the fun that the original Sonic games provided.

What they've been able to do with the Doom engine by merging in Sonic is definitely impressive. It's continually updated too, with a brand new version going up recently. SRB2 version 2.2.9 is out with these changes:

• Fixed animated skin colors in OpenGL.
• Fixed an error when loading addons with custom savedata via the command line (notably, when testing from Zone Builder).
• Optimized Lua, plane rendering, and drawing of FOFs.
• Added polyobject support for Lua.
• Added multitag library for Lua, which allows reading and manipulation of tags on mapthings, lines and sectors; also added tag iterator functions.
• Attraction Shield’s homing attack may now be chained.
• The addfile command now supports adding multiple files.
• The player will now smoothly slide across a sloped ceiling.
• Let more graphics lumps be replaced clientside.
• Various bits of progress on UDMF.
• Special text is printed when the player begins the final lap in Circuit mode.
• Ring drain sectors play the ring depletion sound.
• Pausing the game is no longer possible during the score tally screen in Marathon Mode.
• Tons of map fixes from sphere.
• Added acronym keywords to Co-op levels. For use with the map command, so e.g. you can warp to Green Flower 1 with map GFZ1.
• The game now resends the whole gamestate when resyncing a player.
• Fixed an issue with the installer executables where you wouldn’t always be asked where you want to install the game.

Sounds like there's never been a better time to try it out!

Check it out on the official site. Available for Linux on Flathub.