CRYPTOCard Network Security  
   Password tokens delivered on key fobs, palm pilots, hardware or software. Security for dial in, access control, internet and web connections. Offers a strong two factor system. Management software. Includes rationale and business case for token-based acce
   http://www.cryptocard.com/

Clearview Systems  
   Suppliers of Secure Computing SafeWord, a scheme based on hardware tokens. Includes rationale for single-use password systems, as well as other network security products.
   http://www.clearview.co.uk/

One Time Passwords In Everything (OPIE)  
   OTP (S/Key) source code, oriented towards unix servers. Provides calculator tools, as well as server FTP, login and su programs. Freely redistributable. Site includes user-contributed software.
   http://inner.net/opie

JOTP Calculator  
   A java applet OTP (S/Key) calculator. The applet downloads onto the client machine and calculates locally.
   http://www.cs.umd.edu/users/harry/jotp/

The S/KEY One-Time Password System  
   Scholarly paper by Neil Haller on the original S/Key system. Links to many citations from the original paper.
   http://citeseer.nj.nec.com/34338.html

SkeyCalc  
   OTP (S/Key) calculator for MacOS X, MacOS X Server and NEXTSTEP. RFC-2289 compliant. Site includes software downloads, documentation and an introduction to the technology.
   http://www.orange-carb.org/SkeyCalc/

PalmKey  
   OTP (S/Key) calculator for palm pilots. Site includes information about both source and binary distributions.
   http://palmkey.sourceforge.net/

OTPC 9000  
   An OTP (S/Key) calculator for Nokia 9000 cellular phones. Includes S/Key information and resources.
   http://www.basun.net/software/otpc/

David Baldwin  
   Author of an Apple Newton OTP (S/Key) calculator. Site includes information about the author, and a link to his FTP site.
   http://tltsu.anu.edu.au/~dgb900/

DynaPass  
   Provides primary or secondary authentication by regularly distributing passwords (or parts of passwords) through wireless phones. Time locked access.
   http://www.dynapass.com/

IETF One Time Password Authentication Charter  
   Current specifications for the official internet standard (a continuation of the BellCore S/Key standard). Composition and membership information included.
   http://www.ietf.org/html.charters/otp-charter.html

PyOTP  
   A simple Python library, currently under development, to generate OTP (S/Key) responses. RFC-2289 compliant. Includes links to development and release information.
   http://pyotp.sourceforge.net/

S/Key Introduction  
   A technical description of the S/Key algorithm.
   http://www.surfnet.nl/innovatie/surf-ace/security/doc/skey.html

RFC2289 - A One-Time Password System  
   The current internet standard, as descended from the original S/Key specification.
   http://www.faqs.org/rfcs/rfc2289.html

pilOTP  
   OTP (S/Key) client for the Palm platform. Includes screen captures, and general information as well as software downloads.
   http://astro.uchicago.edu/home/web/valdes/pilot/pilOTP/

otpCalc - An OTP and S/Key calculator for X  
   otpCalc is an RFC2289 and RFC1760 compliant one time password calculator, written to use the GTK+ library for screen I/O.
   http://killa.net/infosec/otpCalc/