[antihero]

I'd be interested to see how the royalties work when UE for is not the primary part of the product.

Say, hypothetically you had an advanced visualisation component that you wanted to build in UE, or a virtual tour part of a much larger app. Or even using it to provide some sort of AR experience, however this was just one feature of a much much larger project, which revenues could be in the millions. Does that mean they get 5% of the whole thing? Or just the part that directly relates to the game engine?

Not knocking it, I think it's a great model, but it does make for an interesting problem. I think Unity is a better choice for this sort of scenario, of course, but still.

[frontier]

Back when UE4 was first released I asked that question in relation to training simulations within larger courses and the answer was that, as no software was being sold, then no royalties would apply! (just the $20/mo subscription cost at the time) Definitely contact EPIC and get a ruling on your specific case, but I was blown away! In the end we didn't go ahead with those simulations as the html5 support wasn't quite ready at the time.