Apple has released the third beta versions of iOS 12.1.1 and MacOS Mojave 10.14.2 for users participating in the beta system software testing programs. A developer version is typically available first, soon followed by the same build for public beta testers.
The new beta versions likely focus on continuing bug fixes and security enhancements to the iOS and MacOS operating systems.
Perhaps the most notable adjustment in iOS 12.1.1 beta is that it revises how you flip the FaceTime camera in iOS 12 to again emphasize a more prominent flip camera button which is visible during FaceTime video calls.
MacOS Mojave 10.14.2 beta presumably focuses on bug fixes and feature enhancements, but there are no obvious outward changes.
Separately, Apple has also released the third beta versions of watchOS 5.1.2 and tvOS 12.1.1 for users beta testing system software on their Apple Watch and Apple TV, respectively.
Apple usually goes through several beta releases before issuing a final build to the general public, so the final versions of iOS 12.1.1, macOS 10.14.2, tvOS 12.1.1, and watchOS 5.1.2 are likely a ways out.
The current stable versions of system software for iPhone and iPad is iOS 12.1, and MacOS Mojave 10.14.1 for Mac.