Between Johann Sebastian Joust and Neil Stephenson's Clang, there's been a fair bit of interest in motion-controlled swordfighting games of late. Microsoft Research is getting in on the action, too, but its SwordFight project takes a slightly different approach by working on nothing more than your mobile phone. While there have been similar apps before such as Star Wars: Lightsaber Duel, SwordFight uses a technology called FAR that allows the phones to locate each other using sound. It's pretty simple on the surface — one phone makes a sound, and the other works out distance based on the time it takes for the sound to travel to the microphone.
Microsoft researcher David Chu told Wired that this can be determined down to 2-centimeter accuracy, though you score points in SwordFight by bringing your 'weapon' within 15 centimeters of your opponent's. Steel-on-steel swordplay is out, then, but it could prove useful for conflict resolution at times when you forgot to bring your motion controller. Unfortunately Microsoft doesn't have any plans to release the game to the public right now.