Unreal Engine 2 Runtime Demo is a free (for non-commercial and educational purposes) version of engine used to create the game Unreal Tournament 2004. Basically it is the game stripped off all the game content. You can still develop a mods in UnrealScript, but you cannot use any game content available in Unreal Tournament 2004.
More information about Unreal Engine 2 Runtime Demo can be found here: UnrealEngine2Runtime.
Information about installation: Documentation.
More information about Unreal Engine 2 Runtime Demo can be found here: UnrealEngine2Runtime.
Information about installation: Documentation.