[mikegerwitz]

Wow...nostalgia going strong. These screenshots bring me back.

https://openrct2.website/getting-started/index.html

"OpenRCT2 needs the object files (containing graphics, sounds and models) from the original RollerCoaster Tycoon 2 to work. You'll need to have a copy of RCT2 before beginning."

[Cthulhu_]

After a number of years, the OS version of Transport Tycoon allowed developers to use their own graphics package; they made and open sourced one of those, so needing a copy of the original game was no longer necessary.