GREPOLIS is an advertised free MMO browser Game that has recently brought over to the US servers. The object of the Game is to build cities and a military that can conquer and take cities away from other Players. You must work with other Players forming alliances and eventually take control of the many islands that make up the Game map. Each island contains space for twenty city slots and once your alliance controls an island, you can build a world wonder near the end game. To get to the end Game will take roughly two years depending on the number of Players and the number of cities built. This Game is always active. If you are not online and playing you can still lose your cities to other Players. Another downside to this is there is no option to hide your armies. You can, however, install an app to play the Game on your phone while you are away from the pc and it has an option that will notify you if you are being attacked, but unless you are ok with being woken up at 4 am, best to leave it off.
GREPOLIS is an online browser game and should run smoothly on practically any PC with a updated web-browser.