FreeBSD is by far the most popular version of BSD, the legendary operating system that has contributed a great deal to every version of Unix® in use today (including Mac OS X). Originally a community effort by the University of California at Berkeley, FreeBSD was aimed at making Unix a little friendlier and easier to use. By the time other free operating systems came along, BSD was firmly established and very reliable. And it continues to be today.
For seven years, the FreeBSD community has relied on Greg Lehey's classic, The Complete FreeBSD, to guide them through its configuration and administration.