A very fun game that you can download on steam. I believe it costs $10 USD and you might have to have another source game with it like TF2 etc. You can make virtually whatever you want, but it's not a walk in the park like minecraft, it will take some learning, you can download mods for it to give you new features, like a mod that enables to to get Ghost from MW2, then you can spawn him in. It's great. You can do what you want.
If your talking about the Garry mod for minecraft, the only on I know of is the mod made in honor of Garry the slime! Garry the slime is Captain Sparklez ( a famous you tubers) pet! Garry the slime died in a tragic despawning accident. So to honor him a fan of captainsparklez made a mod where you can tame slimes, make slime ingots, make Jerry armor, and much more! I hope this helped you!