For assets (graphics, sound, etc.), yeah. OpenTTD, an older sibling project, eventually was blessed with artists willing to remake all of the assets so the game

For assets (graphics, sound, etc.), yeah. OpenTTD, an older sibling project, eventually was blessed with artists willing to remake all of the assets so the game could be played without the original TTD installed. I think a lot of the charm of RCT2 comes from the specific assets in use and the degree of whimsy and joy they contain, more so than TTD's matter-of-fact trains and planes and such. It's not like these folks are setting out to make a totally free-as-in-beer game that replaces the old one; they just want to be able to fix bugs and add features, and you can't easily do that with the original retail stuff.