Glest is a project for making a free 3d real-time customizable strategy game. The game is available for several operating systems and can be completely modified using XML and a set of tools. The current version includes single player game against AI controlled players, providing two factions for the player to control: Magic and Tech, each with their corresponding tech trees, units and buildings.

TriNecatoR says

9/10 - Agree Disagree

Funny open-source toy :) I've played it on Linux!