Imagine you're in the centre of a city. There are four people (the runners) chasing you (with the exciting moniker 'X') within a large, pre-defined area and they're constantly trying to corner you or guess your escape strategy. However, you can see their positions via GPS on your mobile phone - they, on the other hand, can only see your position every six minutes. Sounds like fun? Germany thinks so - that's where the game, which is called Fast-Foot Challenge, is most popular.

But the creators (Urban Team) have made the game, which is free to download, available to everyone. It's a simple premise, and you only need to pay for your own phone and the GPS connection. The popularity of Fast-Foot Challenge is starting to spread to other countries, too, but press coverage of the game has until recently been limited to its homeland where the title has been featured on a number of national TV channels.

In an effort to show how the proliferation of GPS and web technology has made the world an even more fun place, we sat down for an interview with the game's creator, Tom Nicolai, and we've also had a look at what other GPS and 'augmented reality' gaming potential is packed away inside today's mobile phones.

The first thing we asked Tom Nicolai was whether the motivation behind the game was to get technology to promote a more active brand of gameplay - after all, a 25 minute game of ultimate tag is no mean physical feat.

"Playing the game is very different to other mobile phone games," Nicolai began, "On the one hand, it's definitely more demanding: You have to get out and meet other [people] for real. But on the other hand, playing Fast-Foot Challenge gives players much more and longer lasting satisfaction than common video games. Whatever you do in the game, you do it for real. And after the game, you feel like your capabilities are strengthened and extended. Do you remember the last time you climbed a fence? I do.

"Probably the most distinctive element of the game is that you play in an open and unlimited game world. Sure, you are not allowed to leave the game area of about 1-3 km in the game, but within this area, you can make anything part of your game. It's fascinating to see the things people come up with to win."

And see them you can. The game has a dedicated website (http://www.fastfoot.mobi) which may not be the prettiest of web portals, but it does have a 'live' page where you can watch what Fast-Foot Challenges are happening right now, and see the action play out on a Google Map. Nicolai explained how people's imaginative escapes are often the best indicators of the potential hidden within a simple concept:

"In May, we were on a public play event in Berlin with Fast-Foot Challenge for a couple of days. We planned one game to be quite special, since we had a local hip hop group to play the runners with a presenter on a stage to comment on the live satellite view of the game while it was going on. The plan was that the well-prepared rappers would catch X, a guy we picked from the audience. But it all played out differently. During the show, we could see how well X played and how desperate his chasers were. Afterwards, he told us the etails of his story: first he took the bus to get a good leap. Then, when the rappers nearly got him, he stopped a guy with a motorbike and told him: 'I have got to get away from here. Take me with you!' And finally, he borrowed his girlfriend's bike to return to the stage."

And all of this from a game which is still, technically, in the beta stages - even though it's already picked up awards for innovation. Nicolai comments that in the past 12 months, the much wider availability and lower cost of GPS telephone technology has meant that Fast-Foot Challenge has really been on the cusp of new trends in gaming which use that technology, and this is part of why the format has been so successful. Urban Team are now getting ready to release the first full version of the game which will come packaged with a smoother interface and added features:

"We learnt a lot from this version of the game. In the next months, we will launch the 1.0 version, that we've been building since the beginning of the year. It addresses a lot of shortcomings of the original game and has all the things you'd expect from a complete video game. It will have a complete location-based mobile community system, updated graphics, a tutorial and story line with bizarre characters, and a gorgeous sound track. We're very excited about it and how it will be picked up by the players."

This brand of gaming is still fairly embryonic. Another GPS format 'real world' game, but with a stronger emphasis on augmented reality is Wifi Army, where thousands of players are connected to a central system which lets them know when they are in the vicinity of another player. They can then hunt them down using GPS and 'shoot' them through the crosshair on their mobile phone's camera screen. Delightful.

And in about a month's time iPhone developers Acrossair will release their offering, Virus Killer 360 which shows the gamer the street, park or room they're in on the iPhone's display, but with hundreds of spherical, nasty looking virus molecules flying at their faces. Tapping the on-screen viruses with the (get this) 'surface-to-air vaccine' dispatches the little buggers for good, but since the swarm can get so daunting, teaming up with friends to fight off the pandemic ought to make the game's multi-user functionality a major attraction.

None of the internal designs of any of these games is especially complex. They rely on real people to use the real world environment and come up with the most rewarding scenarios on their own, so in our opinion these games offer a level of human creativity which has for the most part been sorely lacking in many traditional videogames. Plus, they're all reasons to help justify hefty line rental bills, so it's win-win, right?