UNREAL ENGINE 3 (UE3)
UE3 was the leading engine of the previous generation. For new projects, we support UE4.
UNREAL DEVELOPER KIT (UDK)
Unreal Development Kit is the free edition of Unreal Engine 3. We no longer support UDK, and recommend beginning new projects for free using UE4, which brings you all the latest engine features as well as full source code access.