Apple has released the first public beta of iOS 9. Following the release of iOS 9 beta 3 for developers, some members of the Apple Beta Software Program can now download the software to their devices.
This is the first major release of iOS to receive the public beta treatment though earlier this year, Apple did invite a number of members of its preview program to test the release of iOS 8.3, as well as iOS 8.4.
Do note that while this is a public beta, it is not an open beta. You still need to be a member of the Beta Software Program in order to access this early version. Also keep in mind that this is beta software. It is not merely an early preview, completely ready to go. It is still in progress, and as such, some of your apps might not work on it.
If you want to participate in future public beta programs, head over to Apple's Beta Software Program site to sign up.