While a few commands, such as ‘cd’ are built directly into bash; many of the most important commands come from coreutils, a GNU package containing over a hundred commands.

Some are the well known commands such as ‘ls’, ‘mv’ and ‘cat’. While there are some more obscure ones that are not always discovered because there are also more modern programs that can do similar jobs.

http://commandline.org.uk/2007/ten-cool-coreutils-commands/