Widelands is a free strategy game in the same vein as Settlers. Widelands has many of the same features as Settlers and can even import Settlers maps.

In Widelands you are in control of a tribe which typically starts with just a castle, your headquarters, with a finite amount of resources. Your job is to build up your tribe and expand the settlement. This is done by getting your tribe to fetch resources and build various structures such as a lumberjack hut (to get wood), ranger hut (to plant new trees), sawmills (to make planks of wood), bakeries, etc.

Later on you can battle other tribes to gain control of the land.