We surely don't need to tell you that it's 
April Fool's Day, given the preponderance 
of gags around the internet. SEGA decided to get in on the action, announcing on Twitter a new Steam game called 
The Murder of Sonic the Hedgehog. Only it's not actually a joke at all, and you can download and play it right now.
No foolin'; 
The Murder of Sonic the Hedgehog is a visual novel-style adventure/puzzle game where you play as an event aide on a special high-speed train known as The Mirage Express intended to host fancy events. It's your first day on the train, and who should be your guests on your first day but 
the famous hero Sonic the Hedgehog and his friends.
The event that they've scheduled is Amy's birthday party, and the party is to take place as a murder mystery party where each guest has a special role to play, right down to "lore cards" that apparently describe their background and role in the story-within-a-story.
The guests include not only the core Sonic group of Sonic, Tails, Amy, Knuckles, Rouge, and Shadow, but also a few more rarely-seen characters, including Vector and Espio of the Chaotix crew as well as the popular-but-rarely-seen Blaze the Cat who originally debuted in Sonic Rush on the Nintendo DS.
These THINK segments are simply controlled using the keyboard.
The free game has a surprisingly high production value, and the gameplay consists of collecting evidence and interrogating suspects like a detective. It also includes brief action segments called "THINK segments" where you play as Sonic in a simple 2.5D runner game not unlike the oft-forgotten Sega Genesis/Mega Drive title Sonic 3D Blast.
If you're having a hard time on the action parts, you can ratchet the difficulty down.
If you're 
a Sonic fan, or even if you're just curious, you can go check out 
The Murder of Sonic the Hedgehog for 
free on Steam right now.