OpenRA: Red Alert, Command & Conquer, and Dune 2000 Unified

https://www.openra.net/

https://github.com/OpenRA/OpenRA

OpenRA provides native support for modern operating systems (including Windows 10, macOS, and Linux) and high-resolution displays without the need for emulators or unofficial patches. It also features fully integrated online multiplayer.

OpenTTD: Transport Tycoon Deluxe Reborn

https://www.openttd.org/

https://github.com/OpenTTD/OpenTTD

Getting Started https://wiki.openttd.org/en/Main%20Page