OpenRCT2 is an open-source version of Rollercoaster Tycoon 2.
It contains all the features of the original game plus some updates and improvements to the 2003 theme park simulator. In addition to this, the open-source creation also supports Mac and Linux operating systems. You can download the game for your choice of OS here.
While the files themselves are free to download, the game requires you to own a copy of the original game, although these days a copy of Rollercoaster Tycoon 2 can be bought relatively cheaply from GoG or Steam. However, it is possible to use the free demo to get the required files to run the game. This can also be downloaded from the OpenRCT2 website, although the games developers do ask that even if you use the demo to make OpenRCT2 work, you still buy a copy of the original game to support its developer, Chris Sawyer.
The game itself is often described as now being more stable than the original release and has also introduced a multiplayer feature, allowing you to play with your friends.
As with OpenTTD, the game is being constantly updated and improved by the community to ensure that it becomes as good as it possibly can be. If you’re interested in getting involved with the development of the game then have a look at OpenRCT2‘s forums.