Our CFD temperature simulation engine is written in high performance portable C++. It compiles and runs on Linux and macOS (and can run on Windows as well). In production we run it on Linux servers.
Our Blowout simulation engine is written in portable C# code (for historical reasons) and currently runs on both Windows and Linux images (we will use Linux in production). We run it on the Microsoft Azure cloud.
It’s important to note though that specific platform requirements for these engines is not something that users see or experience; everything is wrapped and served through our application programming interfaces on our servers (REST based JSON APIs).