Original Authors:
Davy Temperley: http://theory.esm.rochester.edu/temperley/
Daniel Sleator: http://www.cs.cmu.edu/~sleator/
John Lafferty: http://www.cs.cmu.edu/~lafferty/

Much additional work has been done by many different developers.
The current lead developer is 
Linas Vepstas: http://linas.org/

The SAT parser code was developed by 
Filip Maric <filipmaric_at_gmail.com> 
as a part of the 2008 Google Summer of Code (GSoC) project for OpenCog.

Arabic dictionaries were provided by
Warren Casbeer and Jon Dehdari

Farsi dictionaries were provided by
Jon Dehdari

Russian dictionaries were provided by
Sergey Protasov <svp_at_tj.ru>

Turkish dictionaries by 
Can John Bruce <can.bruce_at_yale.edu>

Support for Hebrew, and a complete overhaul of tokenization:
Amir Plivatsky <amirpli_at_gmail.com>

Some of the people who have contributed patches and fixes include:
(In alphabetical order)

Bill Hayes <bhayes84_at_gmail.com>
Borislav Iordanov <borislav.iordanov_at_gmail.com>
Valery Kholodkov <valery_at_grid.net.ru>
Vikas N Kumar <walburn_at_gmail.com>
Dom Lachowicz <domlachowicz_at_gmail.com>
Per Larsson <tucker_at_algonet.se>
Stephen Leibowitz <librestephen_at_gmail.com>
Marc Maurer <uwog_at_uwog.net>
Evgenii Philippov <efilippov_at_gmail.com>
Sergey Protasov <svp_at_tj.ru>
Sampo Pyysalo <smp_at_is.s.u-tokyo.ac.jp>
René Rhéaume <rene.rheaume_at_gmail.com>
Lian Ruiting <lianlian1022_at_gmail.com>
Murilo Saraiva de Queiroz <muriloq_at_gmail.com>
Fridrich Strba <fridrich.strba_at_bluewin.ch>
Simon Stuart <kraven_at_greycascade.com>
Peter Szolovits <psz_at_mit.edu>
Alexander Tkachuk <alexander.tkachuk_at_gmail.com>
Vincent Untz <vuntz_at_opensuse.org>
Bruce Wilcox <gowilcox_at_gmail.com>