UDK is currently in the process of being phased out. At the moment, Unity is actually the engine of choice if you need a free version. That said, Unreal Engine 4 (UE4) has a new subscription model that is much more affordable for indies than any previous incarnation of the Unreal engine. UE4 can be had, in its entirety,…
I guess it depends on your programming skills. iD Software released the Quake source code under the GNU open source license. Check out Retro Blazer, it's built on the Quake source but replicates a Doom-like shooter [ame=" https://www.youtube.com/watch?v=rqOKRLeKDts"]RetroBlazer - The Laboratory - Alpha demo - YouTube[/ame]…