OS X

Berkeley Software Distribution

Berkeley Software Distribution (BSD, sometimes called Berkeley Unix) is a Unix operating system derivative developed and distributed by the Computer Systems Research Group (CSRG) of the University of California, Berkeley, from 1977 to 1995. Today the term "BSD" is often used non-specifically to refer to any of the BSD descendants which together form a branch of the family of Unix-like operating systems. Operating systems derived from the original BSD code remain actively developed and widely used.

The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the operating system, allowing researchers at universities to modify and extend Unix. The first Unix system at Berkeley was a PDP-11 installed in 1974, and the computer science department used it for extensive research thereafter.

Other universities became interested in the software at Berkeley, and so in 1977 Bill Joy, then a graduate student at Berkeley, started compiling the first Berkeley Software Distribution (1BSD), which was released on March 9, 1978

The Second Berkeley Software Distribution (2BSD), released in May, 1979,^[2] included updated versions of the 1BSD software as well as two new programs

                                                             Richard Stallman founder of GNU project

                                                            Linus Torvalds principal author of linux kernel

                                                     Andrew Tannenbaum author of MINIX 

UNIX

                                                                     Dennis Ritchie
The Unix operating system was conceived and implemented in 1969 at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, andJoe Ossanna. It was first released in 1971 and was initially entirely written in assembly language, a common practice at the time. Later, in a key pioneering approach in 1973, Unix was re-written in the programming language C by Dennis Ritchie (with exceptions to the kernel and I/O). The availability of an operating system written in a high-level language allowed easier portability to different computer platforms. With a legal glitch forcing AT&T to license the operating system's source code to anyone who asked Unix quickly grew and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs. Free of the legal glitch requiring free licensing, Bell Labs began selling Unix as aproprietary product.

Tux is the mascot of Linux

Linux

Linux  is a Unix like operating system.The defining component of linux is the linux kernel, an operating system first released by Linus Torvalds. It is also known as GNU/Linux from the GNU project initiated by Richard Stallman.It is a leading Operating System for mainframe and supercomputers.More than 90% of today's fastest 500 supercomputers run on some or the other variant of linux.
The android system also runs on linux.