You can now invite up to 1,000 testers to beta test your iOS apps by simply sending them an email invitation through iTunes Connect. Once they accept your invitation, testers can install your beta app on their iOS devices, get updated builds, and provide feedback, all within the TestFlight app. Learn more about TestFlight.
TestFlight was acquired by Apple back in February. It allows developers to easily send beta builds to their testers. The service has since been gradually integrated into iTunes Connect.
Apple also recently released an official TestFlight app. More details on the app can be found here.