CocoaCEDICT is a Cocoa interface to the CEDICT Chinese (Mandarin) English dictionary. It supports looking up words by their English definition, Pinyin pronunciation, traditional Chinese text, or simplified Chinese text, and more.
Completion Dictionary is a free Xcode plugin that enhances Xcode's built in code completion mechanism. You simply type a few letters, either the abbreviation of a macro or the initials of a symbol name, and press the completion shortcut. Completion Dictionary will do the rest.
Dilo looks up words at http://dict.leo.org and shows the english/french or german translation of that word.
Excalibur is a Macintosh spelling checker. It will spell check documents created by any text editor such as BBEdit, Alpha, Emacs or MPW. It will also spell check the clipboard, making it a useful spelling checker for mail programs such as Eudora and news readers such as NewsWatcher. It will also work with any word processing program that supports Word Services such as AppleWorks (formerly ClarisWorks) or WordPerfect.
HyperSpell is a menu item that gives quick access to Mac OS X's built-in spellchecker. All you do is click on HyperSpell's icon in the menu bar and enter the word, or words, that you want spellchecked. Words that are misspelled appear with a red underline.
pearDict is a little tool that helps to conveniently access online dictionaries. Best of all it is fully integrated into your workflow.
Pinyin Dictionary transliterates Chinese characters (hanzi) to romanized forms. It supports Hanyu Pinyin, Zhuyin (Bopomofo), MPS 2, Wade-Giles, and Tongyong Pinyin.
RAEutil accesses the online spanish academy royal dictionary (DRAE).
Spelling Bee is a small application that lets you check the spelling of words using OS X's central spelling server. It is useful when using other applications that do not support spell checking, or if you are writing with a pen or pencil!
Spelling Corrector allows you to check words spelling in several languages.
Unihan Variant Dictionary
"Unihan variants" are alternate forms of characters belonging to the "Unified Han," or "Unihan," section of the Unicode standard. The Unihan Variant Dictionary allows a user to enter any character and receive a list of corresponding variants, as well as the following information: unicode code point, pronunciation, and meaning.