A recent Popular Science article showcases the simple yet effective EverTune guitar bridge. Utilizing a spring and lever for each guitar string, the device is able to keep consistent tension on every string, therefore keeping them in tune. You set the initial tuning you want at the bridge using a hex screw, and unless you break a string (or go all Richie Blackmore and break more than just the strings) the guitar will stay in tune, even if you give the tuners at the headstock a few turns. You can also adjust intonation and action, again using screws set into the device. The EverTune bridge sells for $330, not including installation. –Mike Bauer
