OpenLoco
An open source re-implementation of Chris Sawyer's Locomotion
...CSL was originally written in x86 assembly, building on top of the RollerCoaster Tycoon 2 engine. However, the engine has changed substantially enough that OpenLoco currently does not share its codebase with OpenRCT2. The reimplementation efforts of OpenLoco are gradual, aiming to ultimately rewrite the entire game in C++. In the earlier years of the project, the in-game UI has been completely reimplemented, and most of the underlying data and object structures have been uncovered. Recent efforts have focussed on reimplementing the game (command) logic.