Avalonia
Avalonia is a cross-platform UI framework for building desktop applications that run on Windows, macOS, Linux, iOS, Android, and WebAssembly. It uses XAML for declarative UI design and supports the MVVM (Model-View-ViewModel) pattern, similar to WPF (Windows Presentation Foundation). It is open-source and built on .NET, enabling developers to create native-looking applications with a single codebase.
Developers should learn Avalonia when they need to build modern, cross-platform desktop or mobile applications using .NET, especially if they have experience with WPF or XAML-based frameworks. It is ideal for scenarios where targeting multiple operating systems (like Windows, macOS, and Linux) is required without maintaining separate codebases, such as for business tools, media players, or productivity apps. Its support for WebAssembly also allows deployment to web browsers, expanding its use cases.