The Uno Platform is an open-source UI platform released under the Apache 2.0 license for single-codebase applications for Windows, WebAssembly, iOS, macOS, Android, and Linux.
Developers can maintain pixel-perfect control over where pixels go while having a choice of developing a platform-specific or custom look and feel of your application. For example, a button will use the original UWP/WinUI style to draw the same look-and-feel button on desktop, mobile, and web platforms.
Uno Platform uses XAML styling to easily target native controls, if desired, on each individual control on-screen. The newest release of the platform is version 3.9, which brings support for .NET 6 (for iOS, Android, mac Catalyst, and macOS), support for Visual Studio 2022 templates, WinAppSDK 0.8.1, Focus management updates, and a XAML Trimming feature to reduce the size of WebAssembly apps.
The move to .NET 6 means that the more straightforward SDK-style projects are used for most except UWP. This allowed the developers behind the project to merge all mobile targets into one project. Additional details on the Uno Platform are available here.