I'm eternally surprised by what modders manage to do with Grand Theft Auto IV, especially as Rockstar never released official mod tools. Modders needed to build tools before they could build mods, a bit like Minecraft--only you end up with high-fidelity murder rather than a monolithic phallus.
The latest wonder rising from GTA 4 borrows an awful lot from another open-world murder simulator: Watch Dogs. Mass-murderer-with-a-heart-of-gold Aiden Pearce is now hacking Liberty City with his magical telephone, popping barriers out the ground, riding trains, spying through cameras, screwing with traffic lights, and generally hacking the planet. It's a remarkable feat.
The creators of the #WatchDogsIV mod say it's "inspired by" Ubisoft's game but insist it's "not a copy," but it does borrow an awful lot (assets included, it seems). You can overload the power grid to cause a blackout, make ATMs spray money to draw crowds that'll inevitably start fighting each other, burst lights, futz with traffic lights to cause pile-ups, set off car alarms--you know, Watch Underscore Dogs stuff. But in a different game with a different simulation, where this won't all work entirely the same. Also you get to be Captain Boringpants and hit men with sticks and do that whole 'pulling your mask up' thing.
Download Hash Watch Dogs IV here. Installation is simplified by using the OpenIV package installer, though the makers suggest a few extras you might too. Combine it with a fancy graphics mod or two and lawks, you'll have yourself a right treat of murder and datacrime for the weekend!