Amnesia Multiplayer (Cringe as you may.)

[Traggey]

I wouldn't know about Grand Theft Auto, I had never heard of such a mod before this.

However again, the engine that game was built on was much more of a high priority engine for its time, and getting something like an open world game alike JC2 or GTA would not be quite as hard as something physics based such as Amnesia. The only real reason I would see to develop anything on the HPL2 engine would be physics interaction, and that's VERY hard to do in MP even with the source code, it's why we see things like Client Sided ragdolls in games.

And making a multiplayer mod for amnesia that would not be used to the main story of the game itself sounds like nothing but a waste of time, as you could with much less effort create something just like that using Unreal3 or Unity3D.