CorsixTH - https://github.com/CorsixTH/CorsixTH
A modern platform's clone of the 1997 Bullfrog game Theme Hospital, where you manage a series of hospitals. CorsixTH is mostly feature complete, with additions like player made maps and levels, and some ease of use changes. The game logic and layout is in Lua, the backend is C++. We have some issues marked Good First Issue, and long term plans including multiplayer. The documentation and wiki are good, and there's a Matrix/Discord room. Also an Android port - https://github.com/alanwoolley/CorsixTH-Android