SerenityOS is an open source Unix-like operating system project with its own custom kernel, graphical user interface, system libraries, and userland tools. It combines a nostalgic “90s UI aesthetic” with modern system capabilities: a preemptive, multi-threaded kernel, own browsers, network stack, file systems, IPC, security features, and a suite of graphical / developer applications. The project is both a hobbyist OS and a polished engineering sandbox.