Open source RTS game built on top of the Spring RTS Engine
https://www.beyondallreason.info/download
You will need a lobby for the Spring Engine, such as SpringLobby. Once this is set up, go to your Spring data folder, and check out a copy of the game
git clone https://github.com/beyond-all-reason/Beyond-All-Reason.git bar.sdd
The game will now show in lobbies as Beyond All Reason $VERSION