Linux is a robust UNIX-like open source OS. Linux is available as a free download, and third-party distributions such as Red Hat Linux provide a variety of tailored options. Linux Systems account for 32 per cent of the server market. Current estimates indicate that Linux is installed on over 20 million computers, with 50per cent of all Linux software shipped by Red Hat. Approximately 40 per cent of companies in North America and Western Europe use or are testing Linux. Red Hat Linux is the most popular version of Linux.