First discovered back in 2017, Marzipan is an internal code name for a project that aims to adds new developer tools that will enable developers to design and engineer a single application that runs on iPhone, iPad, and Mac. Users saw the first part of this project in macOS Mojave. Mojave included apps like Apple News, Voice Memos, Stocks, and the Home app.
In recent years, there seems to have been a move to web apps as companies look to trim development costs. Web apps have gotten faster and more fully featured, and this has led to a “write once” and ship everywhere approach for desktop applications. Chromebooks have certainly played a part of this strategy as well. Marzipan is aimed at making it easier to write and deploy apps for macOS.
Apple’s Marzipan apps have faced a lot of criticism for being so clunky and alien. They do not use Mac-like navigation or controls, feature awkward button clicks as a substitute for the multi-touch gestures the iPad apps were designed around, and are all single window app experiences.
As part of the 2018 WWDC keynote presentation, Craig Federighi showed off a sneak peek of Marzipan. The rumor is that by 2021, Apple wants developers to be able to submit a single binary to the App Store that will house the necessary logic and interface code to deploy onto iPad, iPhone and Mac.