Cataclysm: DDA does a great job at being a semi-realistic 21th century zombie apocalypse. Vehicles, guns, prepping, martial arts, ridiculous amounts of crafting; it has it all. It's best in genre, IMO.

Cogmind was mentioned elsewhere; robots, guns and commercial-level polish.

(Personally, I'm working on a gun-oriented RL in my spare time, but it's going pretty slow ATM.)