iOS 8 beta 3, labeled build number 12A4318c, was released to Apple developers today via the over-the-air mechanism built into iOS and via the iOS Dev Center (membership required).
The third version of the beta software comes 20 days after the second version dropped on June 17.
According to a MacRumors post (and a growing MacRumors forum thread), the latest version adds new iCloud Drive functionality, an updated Find My Friends app, a new Handoff on/off slider in the Settings menu, an option to millimeter the QuickType keyboard. Also, Shared Photo Streams have been renamed Shared Albums in the Photos app, and Events and albums from Aperture are now available again in the Photos app.
iOS 8 beta builds are intended for developers to test their iOS apps and it shouldn't be installed on production devices.
According to Apple iOS 8 is expected to be released to the public in the fall and many expect it to arrive alongside an expected larger iPhone 6 in the late summer-early fall time frame.