Apple has released MacOS Catalina 1
Apple has separately released downloads for iOS 13 beta 5 and ipadOS 13 beta 5 for beta testers, along with new beta builds for tvOS and watchOS.
Mac users currently running the MacOS Catalina Developer beta can find the latest fifth beta available for download now from Software Update in the System Preferences panel of their Mac.
As always, back up a Mac before installing any system software version. Backup is extra important when running beta software.
MacOS Catalina includes various new features for Mac, including updates to bundled apps such as Pictures, Notes and Reminders, the ability to use iPad as a secondary display for Mac, splitting iTunes into three separate apps for music, TV and podcasts , moving iOS device management to the Finder, a new screen saver option, tight security, lack of support for 32-bit apps, and much more.
Technically, any Mac user can choose to become a beta tester for MacOS Catalina, either by paying the annual membership fee to join the developer program, or by enrolling in the free, public beta testing program.
Knowledgeable users can learn how to install MacOS Catalina public beta here if you are interested, but be aware that system software beta testing is only suitable for advanced users, with adequate backup of all data, and preferably on secondary computers and hardware.
Similarly, it is possible to beta test iOS and iPadOS 13 as well, and interested, advanced users can read how to install iPadOS 13 public beta and follow a guide to install iOS 13 public beta on the iPhone even if they do it forcing them.
Apple has stated that the final version of MacOS Catalina will be available to the public in the fall of 2019, probably in the same timeframe as the final versions of iOS 13 and iPadOS 13.