Battle for Wesnoth - a turn based tactics game in a fantasy setting. It's also available on Steam and itch.io. Coincidentally, version 1.18.0 was released yesterday.
This!
I have so many fond memories of epic Battle for Wesnoth sessions with friends. That was back in High School, 12+ years ago, I still have the itch to boot it up again.
Wargus and Wesnoth both run on the Stratagus engine, which was originally developed as a reimplimentation of Warcraft 2 . The engine split to allow for new games to be made, and the War2 functionality was shunted into Wargus where the project remains to this day