GUID/UUID Generator

A GUID (Globally Unique Identifier) or UUID (Universally Unique Identifier) is a 128-bit value typically displayed with the format XXXXXXXX-YYYY-ZZZZ-AAAA-BBBBBBBBBBBB. The value is comprised of hexadecimal letters (the numbers 0 through 9 and the letters A through F) and is used wherever a unique identifier is needed, typically without a central authority issuing the values.

Anywhere one or more unique identifiers are needed but there is no centrally agreed upon authority issuing the identifiers. These are commonly used in database systems.

Wikipedia: Universally unique identifier
ITU: Generation and registration of Universally Unique Identifiers (UUIDs)