ZìKa is a program that helps you to learn the Chinese vocabulary. It allows you to form and save your own lists of words from individual lessons or groups of lessons from various textbooks and display them for study in many different ways, including viewing them in a number of different Chinese fonts that are installed on your computer.
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.