Unity 5's new full-featured Personal Edition is completely, utterly free to use
Past versions of Unity had a free edition, but it was a crippled version of the engine that lost out on many of the advanced features. Pro users either had to buy a license or pay $75 per month for a subscription.
No more. At GDC Tuesday, Unity announced "Unity 5 Personal Edition":
"Unity 5 Personal Edition is a free solution empowering hobbyists, sole developers, and studios just getting started with all the powerful features found in the Unity engine and editor such as Profiler, Occlusion Culling, Render-to-Texture, and Post-Processing Special Effects as well as all the big Unity 5 features like Physically-based Shading, Enlighten, and reflection probes."
In layman's terms: The free version of Unity 5 is now a full-featured version of Unity 5. And there's no need to pay royalties. It's actually, honestly, legitimately free as long as you make revenue of less than $100,000 or have less than that amount in funding.
The Professional Edition still costs $75 per month or a license of $1,500 for developers who don't meet the sub-$100,000 requirement. You'll also get access to advanced support features like Cloud Build Pro and Unity Analytics Pro.
So to sum up: Unreal 4 is free, but you pay 5 percent royalties to Epic after the first $3,000 your game makes every month. Unity 5 is free as long as you make less than $100,000 a year, but costs a flat $1,500 after that point with no royalties.
Either way, it's a great time to be a game developer.