With X10, you can sell your games and make up to $5000 before you have to buy a $2000 license, if my memory is correct. If you wanted, you COULD use X10 for simulation and training but you'd be severly limited, mainly to walk-throughs. FPSC is mainly for FPSs, as the name implies
Engines like Esperient Creator and Unity are better suited for simulation/training software simply because they're general purpose engines and therefore you can do anything with them (In fact training software and the stuff you describe, is the main purpose of Esperient). The downside of both of them is that you'll need to know at least some programming/scripting, but it's within a reasonable amount. As far as royalties, I don't know about Esperient, but Unity has a free version and you can use it to make games and make money off them, no royalties (well, not until you've made $100k anyways)
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