Zombie survival mod DayZ is to receive an update soon which will see the introduction of dogs. Who, in a similar vein to games like Fallout, will act as a companion and bodyguard on your travels.
Your trusty german shepherd can be given basic orders, but much like the (relatively... aside from the zombies) realistic slant the rest of the game takes, your mileage will vary. New dogs will be largely useless, while those who are more experienced will be able to better take orders.
Which will be fine and all so long as you can't name them. If you can name them, and they die, it'll be more emotional trauma than it's worth.