FreeBSD is a free, open-source, Unix-like operating system based on Berkeley Software Distribution (BSD) Unix. It is the most popular among the BSD-based operating systems, with an installed base of more than 75%. Due to legal constraints, FreeBSD cannot be labeled as a Unix system, although it is compliant with Unix internals and application programming interfaces (APIs). FreeBSD’s licensing terms give developers a high degree of freedom to reuse it, so other operating systems (such as MAC OSX) have reused many FreeBSD codes. Although FreeBSD is not categorized as Unix, MAC OSX does have a formal Unix branding.
FreeBSD is used by millions of users all over the world, as well as some of the busiest sites on the Internet such as Yahoo, Sony Japan, etc
