Free Open Source Game Strategy OAD

Free Open Source Game Strategy OAD - 0 A.D. (pronounced "zero ey-dee") is a free, open-source, cross-platform real-time strategy (RTS) game of ancient warfare. It's a historically-based war/economy game that allows players to relive or rewrite the history of six ancient Western civilizations, each depicted at their peak of economic growth and military prowess. The six factions are: The Hellenic States (aka The Greeks), the Roman Republic, The Celtic Tribes, the Persian Empire, the Iberian Tribes, and the Carthaginian Empire, each complete with unique artwork, technologies and civilisation bonuses.
0 A.D. Web Site

Features

    Completely Free (to download, play, and modify)
    Open Source (Code under GPL2, Artwork under CC-BY-SA v3)
    Cross Platform (Windows, Linux, Mac, partial Android support)
    An Open Source, custom built 3D Engine called Pyrogenesis
    Historically accurate civilisation buildings, units, and names
    In-built unit and map customisation tool called Atlas
    Finely detailed environments with fauna/flora native to each terrain
    Offline single player mode or LAN/Online multiplayer gaming
    Mods support (drop in replacements to create a new UI and unit behaviour)
Download
http://sourceforge.net/projects/zero-ad/files/latest/download