What are the differences between UDK and UE4?

does UDK even have things like marketplace and stuff?

in UE4 you can download awesome free completed game projects made by EPIC. Like the robot running dude and the car racing in the desert or a top down RTS tower defense game. And you can edit it and create your own game out of it.
Its really convenient for folks like me who are so new and clueless.