Widelands

Widelands is a free, open source real-time strategy game with singleplayer campaigns and a multiplayer mode. The game was inspired by Settlers II™ (© Bluebyte) but has significantly more variety and depth to it. Still, it is easy to get started through playable tutorials.
As in these earlier real-time games, the player assumes the role of the leader in a feudal society, overseeing the construction of central buildings, production facilities and connecting roads of a medieval economy.