UnrealScript

They also get the C++ source code.

So only having access to the script would limit me how much?

Without a license you can only add to the game, not change it. As in you get all the header files and all if you pay for the engine, then you can change it for your needs. As in changing the graphics systems, etc.

Without an engine, all you can do is change how the game functions, as in mods and such.

But yes. Epic Games and other companies use UnrealScript in their games. I think it was made to make it easy to add changes without delving to the C++ sources themselves. :)

And depends on your needs. On an UT platform, you can create total conversions, mods or single mutators that change the game's style accordingly.

In example, a TC Red Orchestra was made on the UT2004 platform. After that they entered the mod to a contest and won a license to UEngine. :)

Hmmm. So basically I wouldn't be able to change the game type, like just use the engine to make say a 3d puzzle game or something? That really sucks that the script does not give you access to the other variables. Cause I'm definitely not ever going to be able to pay the hundreds of thousands of dollars for the source code.

No, you can certainly change the game type. The objectives of the game can just be hooked to triggers and such that cause the game to end. You actually have a tremendous amount of flexibility with unrealscript.

Things you cannot do with unrealscript are mainly systems level stuff like:
change how the renderer works: i.e. parallelize it across multiple cores
change how the object partion manager thing works
change the logic of the audio system
etc

Things you can do involve:
rewriting your own AI
creating new weapons with radically different gameplay effects
rewrite the camera: say to a 3rd person damped camera with collision detection
You can rebind keys to an unrealscript function of your own creation.

Basically you only cannot change how core systems work. Otherwise you have pretty much free reign and a lot of flexibility.

The only real penalty you pay by using unrealscript only is performance: unrealscript is about 10-12 times slower than native code that does the same thing.

The advantage you get with the expensive license is the ability to rewrite and optimize the engine itself to better match the performance profile of your particular game. You can also then write all your new game logic in much faster native code instead of in script: this allows better performance and much easier/faster debugging.

-me

Thanks for the responses. I actually have one last question. In order to edit things say NPC max health, or other attributes that do not appear in the propeties window, you need to modify the actor class. However, editing anything in there causes the game to crash. Do I need to make a duplicate of the actor class, or is this impossible?