In brief: Few things are more frustrating in the software ecosystem than being forced to buy the same product across multiple platforms. This is an issue on gaming marketplaces, digital music shops, and -- of course -- mobile app stores. Fortunately, Apple is working on a feature for its Mac and iOS App Stores that could make this problem go away.
In short, the feature will enable "universal purchases" for macOS, iOS, tvOS, and iPadOS device owners. If you grab an app on, say, your iPhone X, you'll automatically get it on your MacBook Pro as well. Developers do have the ability to opt-out of using this feature manually, and some undoubtedly will for profit reasons, but it's still a great step in the right direction.
This news was first spotted by Twitter user and app developer Steve Troughton-Smith, but he initially thought universal purchases would only be available for Mac and iOS devices. Apple later published its own blog post revealing that the feature would be available on tvOS and iPadOS as well (as long as a given app is multiplatform, of course).
Universal purchases will be enabled by default for new Mac Catalyst apps, and Apple is making some changes to its various App Stores to align with the feature and to make apps "more discoverable."
You can see a full list of those changes here, but to name a couple, the Mac App Store will see its Photography and Video categories combined under one umbrella (Photo & Video), and there will no longer be a "Kids" subcategory within Games.
If you're a developer, you can enable universal purchases on both new and existing apps. If you're not sure how to do so, Apple has published a guide to help you out. For consumers, this is fantastic news, and it should help to alleviate some of the frustration that comes with juggling different versions of the same app.