Enterprise license for non-game application

We plan to use the Unreal Engine for research and development (and perhaps in a later stage for a product) in the field of command & control systems for firefighters, rescue services and police forces.

In the license FAQ, we have read that there is a special “Enterprise” license for non-game development.
We are unsure, if for such use cases the same license models as for games apply: i.e. 5% royalty on gross product revenue after the first $3,000 per game per calendar quarter from commercial products.

To be more precise: can we use Unreal Engine 4.20 free of charge during a testing and development phase during which we do not sell a product, even though we are not intending to develop a game?

Correct. If you do not earn revenue, you do not owe royalties under the UE4 EULA (EULA - Unreal Engine).

Royalties are also not owed under the Enterprise license, which is intended for non-game development. You can review those terms here: Datasmith - Unreal Engine

Most likely yeah you can use it free of charge forever if you really wanted to. If you feel like you need UDN access(Epic support) I’d recommend getting the enterprise license. The UDN is GREAT for the more advanced topics that are out there.