Bourne shell

/bin/sh is where you will find the ubiquitous and somewhat spartan Bourne shell, written by Steven Bourne.

Most shell scripts call on the /bin/sh because of it's very ubiquity. It's been around since the 70's and it's not going to go away anytime soon. This makes shell scripts that use the bourne shell very portable -- if you code a shell script that uses bash or tcsh-only features, you'll soon enough find a system that doesn't have the shell that you wrote it for.