Forge of Empires is a free, browser based game developed by InnoGames. In the game, you can build your own city and develop it throughout the ages, from stone age to the modern and finally the postmodern era. To advance from one era to the next, you have to explore new technologies to unlock new ways to develop your city. In the meantime, you can conquer neighbouring areas for new resources, or you may contact them peacefully.
Some useful tips and information can be found here.