A history (ahem) of command shells in Unix and Unix-like systems.
Each shell appears at the year that it was first announced to the world. For example, S. R. Bourne describes his shell in the Bell System Technical Journal in 1978 but Bell released it to the world in 1979 or so.
A shell uses a solid, black arrow to point to a shell that it borrows source code from. A shell uses a dashed, grey arrow to point to a shell that the former attempts to be compatible with while not using the latter's source code.
A plum-coloured shell has an open, free, or public license.
A green shell had a proprietary or closed license at the time that it was announced. Source for many formerly-closed shells are now available for us to look at. For example, Bell Labs released to source code to UNIX, available in a few links below.
The authors of a shell are the people credited at the time of the shell's announcement.
Author: Kenneth Almquist
Also known as ash.
Author: Brian Fox
Author: S. R. Bourne
Authors: Doug A Gwyn, Doug Kingston, Ron Natalie, Arnold Robbins, Lou Salkind, and others?
Author: Bruce Perens
Author: Bill Joy
Author: Stephen J. Pendergrast
Also known as dtksh
Author: Charles Forsyth
I've corresponded with Charles Forsyth. He tells me that he adapted his shell for MINIX 1 too.
Authors: Paul Haahr, Byron Rakitzis
Korn shell, ksh88, ksh93, ksh93q
Author: David G. Korn
Public Domain Korn shell, OpenBSD ksh
Author: Eric Gisin
Author: John Mashey
Programmer's Work Bench shell, aka Mashey shell
Author: Tom Duff
Author: Ken Thompson
Authors: Ken Greer, Paul Placeway, Christos Zoulas, et al.
Author: Robert Landley
Author: Paul Falstad