The Ubuntu, Mint, Haiku, ReactOS, OpenBSD and Inferno computer operating systems are free of charge to use and free of most copyright restrictions. The most popular free operating systems are versions of Linux, which is similar to the proprietary Unix operating system first developed by AT&T in 1971.
The most popular builds of Linux are Ubuntu and Mint. Ubuntu serves users all over the world in industrial and government applications as well as in home use. Intended to be lightweight, Ubuntu runs smoothly even on old legacy hardware that might otherwise be considered obsolete, which is part of the reason for its popularity in less-developed countries where older hardware is more common.
Haiku attempts to recreate the lightweight BeOS proprietary operating system in open-source form, emphasizing speed and simplicity. ReactOS acts as a full open-source replacement for the Windows operating system, using some of the coding concepts and tools from Linux.
The OpenBSD operating system emphasizes security above all else, which is why it has such a plain, utilitarian user interface. Inferno focuses on network connectivity across devices, allowing users on a network to seamlessly share computer resources and files as though all the computers on the network were one device.