Just in case you didn’t see the further replies, Open RCT is essentially Roller Coaster Tycoon 2, and you can find all the scenarios from RCT1 and RCT2 and download them, for free.

If your question encompasses the broader theme park tycoon genre, and you chafe against some of RCT’s legacy design elements, you might try Parkitecht or Planet Coaster. PC2 just released, though the reviews seem comparatively tepid to the OG, so buyer beware.