like OpenTTD being a nice “rip off” of roller coaster tycoon

Sorry not sure if I’m reading that correctly, but how is OpenTTD a rip off of Roller Coster Tycoon, it’s based on Transport tycoon a game made by the same developer as Roller Coaster Tycoon, released before Roller Coster Tycoon.

It’s paid (one off $15 I think), but has a two week trial but I’ve been using Nine for a few years now, pretty happy with it.