Own This World is a cross between Risk and Civilisation, with a mix of FourSquare or Facebook Places thrown into the mix. Basically, you accumulate one troop in the territory you're currently in with your iPhone per 30 seconds. When I say "currently in", I mean "standing in it with your iPhone and GPS or WiFi tracking". Yes, folks, it uses a real map of the world and you own a part of the real world... virtually of course.
If you have the most troops in a territory, then you rule it. If you own the most territories, you rule the world! Each territory has one resource attached to it, and you get one unit of that resource every night. There are rulers for provinces/states, and some large cities also.
The resources can currently only be used to attack other players... But the catch is, you have to actually physically be in the territory you want to attack and you can't currently move troops from one territory to another. Duke it out in your city, drive cross-country for massive conquests, or just hike out to the country and hope your 3G and GPS signals come in clear :)
I've been playing this game for 2 days and I must say it's quite addictive. It's one thing to play a game like Risk (on the iPhone) and conquer bad artificial intelligence with fake soldiers, quite another to be in a moving car going "oh, I hope we stay in this area for another 30 seconds, then I'll rule it!" and praying for some traffic. Then getting to your destination and watching your troop numbers go up, attack, and own the land that happens to be where you're eating lunch that day.
There's quite a lot of room to grow for this app/game, including building structures, fortifying, and possibly moving troops under certain circumstances. But most definitely, it's a game worth playing!
You can get the game here (iTunes link): http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=344905169&mt=8&ign-mpt=uo%3D6#