Free Boot Managers and Multi-Boot Loaders

Free Boot Managers and Multi-Boot Loaders
If you want to boot more than one operating system ("OS") on a single computer, a boot manager or multi-boot loader comes in handy. The boot loader allows you to easy create and configure a boot menu so that you can select which OS to boot, set a timeout so that a certain OS is booted if no keys are pressed within a certain time limit, and even prevent the booting of certain operating systems on a computer if a certain password is not entered. Note that some operating systems, like most (if not all) of the free Linux distributions already come with their own boot loader that can dual boot / triple boot Linux, Windows XP, Windows Vista, and other systems that you want.
Commercial boot managers, like Terabyte Unlimited's BootItNG and Acronis Disk Director Suite usually provide additional features, like the ability to partition your hard disks and fix partition errors. BootItNG can also clone and/or image (backup) a partition or drive. (If you're getting Disk Director, try using the coupon code 15YEP, which may or may not give you a discount. No harm trying the code anyway.)
Free MultiBoot Loaders
XOSL (Extended Operating System Loader) Boot Manager
XOSL installs itself into a dedicated partition (which you have to create yourself). The initial installation has to be done from real mode MS-DOS (not a DOS prompt window running in Windows). Operating systems that it can boot include MS-DOS, FreeDOS, Linux (with LILO), Windows 95/98/NT/2000, Solaris, BeOS, etc. You can password protect certain boot items, set a automatic boot timeout, install up to 24 operating systems, swap drives, etc.
GAG The Graphical Boot Manager
GAG boots up to 9 operating systems from either the primary or extended partitions. It installs itself into the boot track, has support for a timer to boot a default operating system, includes password-protection for the configuration menu as well as for individual operating systems, has a SafeBoot system where your hard disk is booted even if GAG is overwritten, and supports hard disks of up to 4 terabytes. It is licensed under the GNU General Public License.
Smart Boot Manager
Smart Boot Manager is an OS independent boot manager that searches for drives and paritions, and automatically includes bootable partitions into its boot menu. It includes a scheduler that allows you to boot a particular system at a preset time. It has the ability to boot from CD-ROMs, boot the default boot record after a delay if no keys are pressed within a specified time, place keystrokes into the operating system's key buffer prior to booting it, etc. It also supports the password-protecting of partitions, drive and the administrative screens.
GNU GRUB - Grand Unified Bootloader
This boot loader, used in some Linux distributions by default. It is distributed here in source form; you probably already have the binary version if you are running Linux. It is able to boot multiple operating systems, including Linux, Windows, MS-DOS, etc.
LILO - Linux Loader
LILO is a boot loader used in some Linux distributions. It is distributed here in source form; if you are running Linux, it is possible that you already have the precompiled version on your system. This multi-boot loader can handle Linux, Windows, MS-DOS, etc