Bacula - the Open Source, Network Backup Tool for Linux, Unix, Mac and Windows.

Bacula is a set of Open Source, computer programs that permit you (or the system administrator) to manage backup, recovery, and verification of computer data across a network of computers of different kinds. Bacula is relatively easy to use and efficient, while offering many advanced storage management features that make it easy to find and recover lost or damaged files. In technical terms, it is an Open Source, network based backup program. 

According to Source Forge statistics (rank and downloads), Bacula is by far the most popular Open Source program backup program.

Features -
Bacula supports many features used by large scale, production networks, including:

Network options

TCP/IP - client–server communication uses standard ports and services instead of RPC for NFS, CIFS, etc.; this eases firewall administration and network security
CRAM-MD5 - configurable client–server authentication
GZIP/LZO - client-side compression to reduce network bandwidth consumption; this runs separate from hardware compression done by the backup device
TLS - network communication encryption
MD5/SHA - verify file integrity
CRC - verify data block integrity
PKI - backup data encryption

Client-options

POSIX ACL - needed to restore Windows NT ACE's and Samba servers
Unicode/UTF-8 - cross-platform filenames
VSS - calls Microsoft's snapshot service
LVM - pre-script setup for Linux/UNIX snapshot
LFS - backup files larger than 2GiB
raw - backup devices without a filesystem

Backup devices

pooling - allocates backup volumes according to job needs and retention configuration
spooling - writes backup data to spool until target backup medium is allocated so jobs can continue uninterrupted
media-spanning - such as spanning tapes
multi-streaming - write multiple, simultaneous data streams to the same medium
ANSI & EBCDIC - IBM compatibility
Barcodes - reading tape barcodes in libraries
autoloaders - virtually every tape autoloader available (called autochangers in Bacula)
most tape drives, including DDS, DLT, SDLT, LTO-1-5

Client OS

The client software, executed by a "file daemon" running on a Bacula client, on many operating systems, [2] including:
Linux - most major distributions, including: CentOS, Debian, Fedora, Gentoo, Mandriva, OpenSUSE, Red Hat and Ubuntu.
Solaris
FreeBSD - all released versions
NetBSD
Windows (File daemon supported on all 32 and 64 bit Windows OSes)
Mac OS X
OpenBSD
HP-UX
Tru64
IRIX

Structure
Bacula is designed to be modular so that it can scale to the needs of its operator(s). Any installation contains three kinds of daemonsto execute backup and restore functionality:Director Daemonmanages other daemons, queries and updates catalog, interfaces with operator front-ends, automates backup schedulesStorage Daemonmakes system calls to drive backup media, responds to read/write requests from Director, and receives backup/restore data from file daemonFile Daemonnegotiates client-side communication, encryption and compression, opens file handles to access a client's dataBacula Consolethe control interface from which the user can enter commands to operate Bacula tasks. the console is a command line interface.Bat (Bacula Administrative Tool) Consolea GUI interface from which the user can enter commands to operate Bacula tasks.Tray Monitoris a GUI that can be installed on any desktop to monitor the Bacula operations.Bweba web interface that allows systems management views of all the Bacula backups. It also permits most all operations that can be done with the console.

These daemons can run on independent hosts but typical installations consist of three kinds of Bacula hosts:Client machinesthe machines that contain the files to be backed upStorage machinesmachines that contain the media used to store the backupsBackup Serversthat orchestrate the backup processes

The Director manages everything so is called a "backup server"; the client and storage daemons run as its subordinates and have no direct control of the back up process. While this structure suggests that the three daemons run on three different machines, an equally valid setup is to run all three daemons on the machine that controls the backup process and backup additional machines that have just a file daemon installed. It is also possible to mount remote files and storage resources into the Director's filesystem over SMB or NFS, however, the Bacula developers discourage this in favor of having a File daemon installed on each machine to be backed up. In practice, however, the Director and Storage Daemon are often run on one machine (often referred to as the Bacula Server). The File Daemon is then run on each machine to be backed up (including the Bacula server—because its catalog is dumped as SQL).

Backup data can be stored on various media, including tape, and disk.

Limitations
Bacula stores backup data in an open and documented yet unique volume format; there are Bacula standalone tools to read/write the backup data (bls, bcopy, bscan, bextract), these tools are not compatible with other Unix backup utilities such as tar or dump. The Bacula developers do not consider the unique volume format a limitation, because it is an extensible, machine independent format that surpasses the capabilities of the tar and dump formats.

By default, and as is the case for all other open source backup software, Bacula's Differential and Incremental backups are based on system time stamps. Consequently, if you move files into an existing directory or move a whole directory into the backup FileSet after a Full backup, those files may not be backed up by an Incremental save because they may have old dates. You must explicitly update the date/time stamp on all moved files. Bacula versions starting with 3.0 or later support Accurate backup, which is an option that addresses this issue.[3]

11 June 2012: Bacula 5.2.9 has been released.

Download -
Download bacula-win32-5.2.9.exe (11.1 MB)
Download other version files

Website -
http://www.bacula.org/
http://sourceforge.net/projects/bacula/
http://en.wikipedia.org/wiki/Bacula

Documentation -
http://www.bacula.org/en/?page=documentation

Manual-
http://www.bacula.org/en/dev-manual/main/main/What_is_Bacula.html