Please note Unreal is not free. They charge a 5% royalty, although that royalty kicks in only at $1 million. Copy and paste from their website:
"Unreal Engine is free to download. We offer a choice of licensing terms depending on your use of Unreal Engine.
- Under the standard EULA, Unreal Engine is free to use for learning, and for developing internal projects; it also enables you to distribute many commercial projects without paying any fees to Epic Games, including custom projects delivered to clients, linear content (such as films and television shows) and any product that earns no revenue or whose revenue falls below the royalty threshold. A 5% royalty is due only if you are distributing an off-the-shelf product that incorporates Unreal Engine code (such as a game). Provided that you notify us on time using the Release Form, you will only owe royalties once the lifetime gross revenue from that product exceeds $1 million USD; in other words, the first $1 million will be royalty-exempt.
- There are also options for custom licenses that can include premium support; private training; negotiated terms for lower royalties, no royalties, or a different basis for royalty negotiation; and more. Contact us to inquire about a custom license for either games or non-games use."
Licensing terms: https://www.unrealengine.com/en-US/license