Very broad question but related: this blog [0] discusses how a modelling product was used to simulate the internet backbone. If your aim is real-time reaction modelling of actors, this could theoretically be implemented using such a system.

They have an open beta [1], although building a comprehensive system like that described above seems a very significant task even to a large engineering team.

[0] https://improbable.io/2016/03/24/what-we-found-when-we-simul...

[1] https://spatialos.improbable.io/get-spatialos

(Disclaimer: I have interviewed with and accepted an offer by Improbable)