Verbix
Software for conjugating verbs in modern and extinct languages, including English. Free to use online or pay for the downloadable version.
http://www.verbix.com/

Grammar Slammer
Grammar reference in Windows Help file format. Shareware.
http://englishplus.com/gramslam.htm

WordWeb Developer
Allows you to add thesaurus/ dictionary functionality to your applications.
http://wordweb.info/developer/

iFinger Electronic Reference
Software for Windows, which provides direct offline access to various commercial dictionaries and reference sources. Demos, detailed product information, online ordering.
http://www.ifinger.com

FrKeys
A program for all word processing applications to add accented characters to text. Especially suitable for language departments in educational establishments.
http://www.edhitec.com/edhitecedhome.htm

Groan
A text mode menu and window-driven user interface for dictionaries. Includes a dictionary manager, quick word lookup, and configurable color schemes.
http://konst.org.ua/groan

Numberator
Convert numbers and currencies into words. Supports 17 languages and 93 countries.
http://webs.sinectis.com.ar/alejand/num/numberator.htm

Grammarian
Universal interactive grammar checking, spelling checking, dictionary, thesaurus, autocorrect, and autotype tool that works with virtually every program on your Mac computer.
http://linguisoft.com

Editor
Proofreads text for grammar, spelling, style, and mechanics errors and problems ignored by major word processors' checking tools. Provides examples, explanations, and suggestions.
http://www.serenity-software.com

Cypress Media Group: Software for Writers
This site offers writing software designed by professional writers and editors. Learn the secrets of writing in a clear, concise and correct style.
http://www.cypressmedia.net/editorsoftware/affiliate_index.html

Wordz Toolbar
Free, instant, one click access to dictionary and thesaurus definitions and spell checking from a toolbar on your web browser. By Socket Software.
http://www.socketsoftware.com/Products/wordz/

Online AsifSound To Spelling Dictionary
Input- abstract easy symbols of American word pronunciation. Output- corresponding spellings.
http://www5d.biglobe.ne.jp/~the_imai/online/a2spelling.htm

Oleander Solutions: Readability
Readability software package used for analyzing and improving your documents.
http://www.oleandersolutions.com/readabilitystudio.html

ProofreadingTools.com
Proofreading tools for Microsoft Word and PowerPoint.
http://www.proofreadingtools.com