Unreal Engine
The latest generation is Unreal Engine 4, which was launched in 2014 under a subscription model. Since 2015, it can be downloaded for free, with its source code available on a GitHub private repository. Epic allows for its use in commercial products based on a royalty model, typically asking developers for 5% of revenues from sales, though with the success of "Fortnite", which has become a testbed for Unreal Engine for Epic, Epic waives this fee for developers that publish their games through the Epic Games Store. On May 13, 2020, Epic announced that their portion of royalties for games developed in Unreal Engine are waived until developers have earned their first in revenue, retroactively applying to January 1, 2020. Unreal Engine 5 is scheduled for full release in early 2022.