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.
https://en.wikipedia.org/wiki/Almquist_shell
Author: Brian Fox
https://en.wikipedia.org/wiki/Bash_(Unix_shell)
Author: S. R. Bourne
https://en.wikipedia.org/wiki/Bourne_shell
https://archive.org/details/bstj57-6-1971
Authors: Doug A Gwyn, Doug Kingston, Ron Natalie, Arnold Robbins, Lou Salkind, and others?
https://web.archive.org/web/20040227010520/http://web.cs.mun.ca:80/~michael/pdksh/CONTRIBUTORS
Author: Bruce Perens
https://en.wikipedia.org/wiki/BusyBox
Author: Bill Joy
https://en.wikipedia.org/wiki/C_shell
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.
https://web.archive.org/web/20040227010520/http://web.cs.mun.ca:80/~michael/pdksh/CONTRIBUTORS
Authors: Paul Haahr, Byron Rakitzis
ftp://ftp.sys.toronto.edu/pub/es/old/
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.45.8024
https://stuff.mit.edu/afs/sipb/user/yandros/doc/es-usenix-winter93.html
Author: David G. Korn
https://en.wikipedia.org/wiki/KornShell
http://www.kornshell.com/info/
Author: ?
https://en.wikipedia.org/wiki/MirOS_BSD
Author: Eric Gisin
https://web.archive.org/web/20040227010520/http://web.cs.mun.ca:80/~michael/pdksh/CONTRIBUTORS
Author: John Mashey
Programmer's Work Bench shell, aka Mashey shell
https://en.wikipedia.org/wiki/PWB_shell
https://grosskurth.ca/bib/1976/mashey-command.pdf
https://groups.google.com/forum/#!original/net.unix-wizards/k1FW4s0X7jw/4GNAGTPHLXQJ
Author: Tom Duff
https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs
https://en.wikipedia.org/wiki/Rc
http://doc.cat-v.org/plan_9/4th_edition/papers/rc
http://citeseerx.ist.psu.edu/viewdoc/versions?doi=10.1.1.47.1625
Author: Ken Thompson
https://en.wikipedia.org/wiki/Thompson_shell
https://www.bell-labs.com/usr/dmr/www/hist.html
Authors: Ken Greer, Paul Placeway, Christos Zoulas, et al.
https://en.wikipedia.org/wiki/Tcsh
https://github.com/tcsh-org/tcsh
https://groups.google.com/forum/?hl=en#!msg/net.sources/BC0V7oosT8k/MKNdzEG_c3AJ
https://www.usenix.org/legacy/publications/library/proceedings/tcl96/full_papers/korn/index.html
Author: Robert Landley
https://en.wikipedia.org/wiki/toybox
Author: Paul Falstad
https://groups.google.com/forum/#!msg/alt.sources/tVgN49u8Ax4/7VgQlHZ4bJMJ
http://zsh.sourceforge.net/FAQ/zshfaq01.html#l1