GNUstep

GNUstep is an open-source software framework that provides tools for building and running applications similar to those on macOS, using a technology called Objective-C. It aims to create a free, compatible alternative to Apple's Cocoa framework, enabling developers to create cross-platform applications for Linux, Windows, and other operating systems. GNUstep offers a set of libraries and interfaces that help developers design user interfaces and manage application features consistently across different environments, fostering software freedom and collaboration within the open-source community.