Nisus Thesaurus 1.0 a free download
After a period of beta testing, Nisus Software has released Nisus Thesaurus 1.0, an electronic thesaurus that automatically integrates with any Service-aware Mac OS X application including Nisus Writer Express, Mail, TextEdit and Safari.
Nisus Thesaurus is based on the WordNet lexical database. Features include a 120,000 word database, Cocoa-based interface, a built-in glossary, an "offensive words" filter and more. Cocoa is Apple's object-oriented development environment.
Nisus Thesaurus is a free download. System requirements are a Power Mac G3 or better and Mac OS X 10.2 ("Jaguar") or later. Nisus says it's also compatible with Panther (the upcoming Mac OS X 10.3).