 FreeBSD is a free Unix @-@ like operating system descended from Research Unix via the Berkeley Software Distribution ( BSD ) . Although for legal reasons FreeBSD cannot use the Unix trademark , it is a direct descendant of BSD , which was historically also called " BSD Unix " or " Berkeley Unix " . The first version of FreeBSD was released in 1993 , and today FreeBSD is the most widely used open @-@ source BSD distribution , accounting for more than three @-@ quarters of all installed systems running open @-@ source BSD derivatives . 
