macOS Catalina (version 10.15) is the fourteenth major release of macOS, Apple's desktop operating system for Macintosh computers. It is the successor to macOS Mojave and it was announced at the WWDC 2019 on June 3, 2019.
System
Catalyst
Catalyst is a new platform allowing software to target both macOS and iPadOS. Apple demonstrated several ported apps, including Jira and Twitter (after the latter discontinued its macOS app in February 2018).
Gatekeeper
Mac apps, installer packages, and kernel extensions that are signed with Developer ID must now be notarized by Apple in order to run on macOS Catalina.