The iOS 13.4 developer beta includes nine new Memoji Stickers (expressing celebration, eye rolling, and huffing with anger, among other emotions) for Messages, FaceTime, and other apps that use your phone's keyboard. CarPlay also has some new features, including further support for navigation apps outside of Apple Maps and more phone features, like seeing call controls on the dashboard during a call via the phone app.
After being delayed since last fall, both the iOS 13.4 beta and the MacOS 10.15.4 beta finally got iCloud Folder Sharing -- allowing you to share folders with others via iCloud Drive directly from the Files app on your phone, or from Finder on Mac. Similar to Google Docs, you can give people editing or read-only access. You can also limit access only to those you invite to view the document, or to those you share a link with. These folders can be accessed from iPhone, iPad, Mac, Windows (via iCloud for Windows) or iCloud.com.
Otherwise, the MacOS beta includes new screen time communication limits, to help parents control who their kids talk to, and when. Apple's head pointer technology -- previously seen in iOS -- is coming to MacOS Catalina as well, allowing you to move your head and the Mac camera to move your pointer along with it to improve accessibility.
Another major update: Starting in March 2020, developers will be able to create one app that gets distributed to iOS, MacOS, iPadOS, and TVOS with just one purchase. As a customer, that means if you buy one version of the app, it will automatically unlock across all of those OS platforms, instead of requiring you to download a different version for each one. This follows up on the promise of Mac Catalyst -- software unveiled at WWDC 2018 that would make it possible for developers to move iPad apps to the Mac by simply "checking a box" in the development program Xcode.
Apple released the public version of iOS 13.3.1 last week. Developers who are registered with Apple can download the iOS 13.4 beta now. For everyone else, the public beta for iOS 13.4 is expected to be released on Thursday.