Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive.
These are based at least partially on Ubuntu, which is based on Debian: Microsoft representatives have described third-party efforts at producing Windows-based live CDs as "improperly licensed" uses of Windows, unless used solely to rescue a properly licensed installation.
The following products are based upon Illumos: This list is for operating systems distributions that are specifically designed to boot off a (writable) USB flash drive, often called a USB stick.
(This does not include operating system distributions with a simplified "installer" designed to boot from a USB drive, but the full OS is intended to be installed on a hard drive).
In addition, many other operating systems can be made to run from a USB flash drive, possibly using one of the List of tools to create Live USB systems.