After GOG it is now also free on itch.io, as part of the "Free as can be" promotion for International Workers' Day.
From the website:
In a dystopia where wealthy capitalists control elections, media, and the lives of working people, we’re faced with two choices — accept it or fight for something better.
Tonight We Riot doesn’t have just one hero. Instead, you play as a movement of people whose well-being determines the success of your revolution. It features:
Couch co-op (Online co-op works with Parsec)
20 unlockable weapons, gear, and perks
A dog
Whimsy
Kaiju
A wood chipper
Endless Mode
Horror Synth
The unique catharsis that comes from throat-punching a billionaire ghoul who would rather watch the world and everyone on it burn than lose a tax break.
Enjoy!
Link to GOG post