http://tkoc.net
I have been playing this game off and on for ~3 years. It doesnt compete with RTS games or anything but its fun and has a nice community.
The gist of it is this:
You have a province within a kingdom. Your province has certain resources: a gold, metal and food income as well as a peasant population. You use this income to purchase units and build buildings. You increase the size of your province by attacking other players.
Its quasi-turn based. Once every hour everything updates, you get all of your resources for that hour and all actions happen. What really attracted me to it is you can do pretty decent by playing 10 minutes 1-2 times a day.. or if you get into the politics it can consume as much time as you like. So in this way its very versatile for a busy schedule.
If your interested in playing IM me on AIM or MSN and I'll give you some help. The main reason I am posting this is because the game has never been advertised really and without the link clicking other games feature its hard to get new players in the community.