updated 01:36 pm EDT, Mon July 8, 2013
Release notes mention only bugfixes, compatibility issues
Apple has released a third beta of iOS 7 to developers, available either through iOS' Software Update function or the official iOS Developer portal. Any feature additions have yet to be discovered, but release notes mention a variety of bugfixes and known issues. Some existing features, such as AirDrop and iCloud Keychain, are not compatible with their beta 2 counterparts.
So far Apple has maintained a two-week gap between iOS 7 betas, the previous one having been seeded on June 24th. Accompanying beta 3 is a third developer preview of Xcode 5, the forthcoming upgrade of Apple's development software for OS X and iOS.
The finished version of iOS 7 is due sometime this fall. The common forecast is September, alongside new iPhones, iPads, and iPods.