wxWidgets
wxWidgets is a free and open-source C++ framework for developing cross-platform graphical user interface (GUI) applications. It provides a native look and feel on each supported platform by using the underlying operating system's native widgets, while allowing developers to write code once and deploy it on multiple systems including Windows, macOS, Linux, and others. The framework includes a wide range of GUI controls, as well as utilities for file handling, networking, and threading.
Developers should learn wxWidgets when they need to create desktop applications with native performance and appearance across multiple platforms without relying on web technologies or virtual machines. It is particularly useful for C++ developers building tools, utilities, or complex software like IDEs, media players, or scientific applications where platform integration and performance are critical. Its mature codebase and extensive documentation make it a reliable choice for long-term projects.