The Third sun

Battle for Wesnoth is an open source, turn-based strategy game with a high fantasy theme. It features both singleplayer and online/hotseat multiplayer combat.

BFW support custom campaign creation, here is one :

The third sun

In the Wesnoth Lore, humains has created a second sun to avoid darkness forces invasion. They are now about to set a third one ! You are a nagolh, an alien race weaked by the sunlight. You just eard about the third sun summoning and decide to drive your spaceship to the humains planet and stop them ! 

This is a custom campaign also named as MOD. I made custom tiles, maps, units and interactions.