Windows Alternative is a term used to describe operating systems that are alternatives to the Windows operating system. The most popular alternatives are Linux, Unix, and IOS. Linux is an open-source operating system that is free to use and is based on the Linux kernel. Unix is a multi-user, multitasking operating system that is used in many large-scale computing environments. IOS is a mobile operating system developed by Apple Inc. for its iPhones, iPads, and other devices.