OpenRCT2 is a free open source version of RollerCoaster Tycoon 2. It is strongly based on the original game and therefore looks like, and plays like the real deal. The game is rewritten into a modern language allowing people to extend and improve the game. Just like what happened with Transport Tycoon Deluxe which got remade into OpenTTD through a similar procedure. OpenTTD now has thousands of new future-proof features and OpenRCT2 will walk that path too eventually.