Many discs are meant to have their software run automatically when booted, rather than first being installed on a hard drive. These are analogous to boot floppies back from the DOS era, which were used to flash the BIOS or to save memory which would be taken up by terminate and stay residents.
A utility for wiping and permanently removing data from hard drives. Doing so also helps determine whether a hard drive is in good condition. Our standard procedure is to wipe one hard drive at a time, typically on a machine set up for that purpose and to use the AUTONUKE option.
The original Linux liveCD. It had no capability to be installed, at least at first.
A lot of boot only linux discs, such as "Parted magic", "insert" and "SystemRescueCd" are designed as utility sets specialized for system maintenance and the like.
Ultimate boot CD
Not to be confused with UBCD for windows. A collection of diagnostic and other tools: such as memtest. Recent versions also include the linux distro "Parted magic".