You can use either Unity or Unreal Engine - both are free to develop. They cut into your returns, though.

Some people are talking about app building. Unity and Unreal 4 are both game engines which means they run simulations. Since they use C# and C++ among other languages, and the target is desktop PC, you can run any software. They both also have other ways to write logic with triggers or blueprints, etc.

You could develop for WebVR (https://mozvr.com). That way you can publish whatever you want, no gatekeepers, and will eventually have instant distribution to anyone with a browser and headset.