Without the internet, you cannot chat with other players. A chat is more than just a console, that's why I asked you to clarify.
What you want is a console with a cheat system - a chat system needs the internet and cannot exist without.
(and a chat system with internet will probably be impossible for you, as you would not only need internet scripts (of which are only very basic variants available) but also a server (which you would have to pay for and program the server-side of the chat)
However, making a cheat system with a console requires at least two scripts, one for activating a console and one for full keyboard support.
Those scripts already exist on the master script list, but if you're a beginner to RM, I would really suggest you only use scripts if really neccessary.
Is there a reason why you want a console for cheats? There are several other ways to make evented cheat systems, or even make cheat items that can change values at will.
That said - in case you didn't know you need full developer access to a project to add a cheat system, which means you can only do this for your own games, not for other's games.