aka "Bourne" shell, written by Steve Bourne at AT&T Bell Labs for Unix V7 (1979).
Small, simple, and (originally) very few internal commands, so it called external programs for even the simplest
of tasks. It is always available on everything that looks vaguely like Unix.
The "C" shell. (Bill Joy, at Berkeley).
Many things in common
with the Bourne shell, but many enhancements to improve interactive use. The internal
commands used only in scripts are very different from "sh", and
similar (by design) to the "C" language syntax.
The "Korn" shell, written by David Korn of AT&T Bell Labs (now AT&T Research).
Written as a major upgrade to "sh" and backwards compatible with it, but has many internal commands for the
most frequently used functions. It also incorporates many of the features from tcsh which enhance
interactive use (command line history recall etc.).
POSIX 1003.2 Shell Standard.
Standards committees worked over the Bourne shell and added many features of the Korn shell (ksh88) and
C shell to define a standard set of features which all compliant shells must have.
The "Bourne again" shell. Written as part of the GNU/Linux Open Source effort, and the default shell for Linux and
Mac OS-X. It is a functional clone of sh, with additional features to enhance interactive use,
add POSIX compliance, and partial ksh compatability.
A freeware functional clone of sh, with parts of ksh, bash and full POSIX compliance, and
many new interactive command-line editing features.
It was installed as the default shell on early MacOSX systems.