GRML is a bootable live CD Linux distribution intended for system administrators and anyone else who has cause to maintain or repair computers. As a Live CD, it does not install anything to your hard disk (you don't even need one) running entirely from the CD. This makes it ideal for system rescue, recovery and repair, and it contains all the tools you need to repair both Linux and Windows systems, even when they are too broken to boot.
Compression techniques enable GRML to store about 2.3GB of software and documentation on a 700MB CD. this provides a full desktop environment with Internet tools (so you can use your favourite search engine to find help when dealing with a problem) as well as all the diagnostic and repair tools you could need.
If you need to use it on a computer without a CD drive, such as a netbook or server, there is a program to transfer GRML to a USB stick, so you can have a complete rescue environment on your keyring. If you don't need a full desktop environment, there are smaller versions with either a less featured desktop (grml-medium) or a text-only version for power users (grml-small). All of these are available in 32 bit and 64 bit variants. If you only choose one, go for a 32 bit version as this will also work on 64 bit hardware.
A useful addition to any self-respecting sysadmin or geek's toolbox. Get it now to have it handy should disaster strike.