Age of Empires Online

Age of Empires Online (abbreviated AoEO), is a history-based RTS. The game is free-to-play—it is free for users to play, with the additional option of earning or purchasing premium content. Premium content may include access to many special items and blueprints, and more quests and features. Also, booster packs are now available, such as Defense of Crete and Skirmish. This former gives the player the ability to play in a survival type mode game, while the latter allows up to four humans versus up to four CPU opponents in a more traditional skirmish gamemode. (Soure: Wikipedia)