WordNet and Wordage
I was checking for updates to WordNet, a thesaurus program that I use, when I found a similar tool on-line: Wordage. There’s no explicit information there about the dictionaries behind the Wordage interface, but I suspect WordNet was involved. Wordage looks very handy, especially compared to the current state of WordNet usability.
WordNet is now at version 3.0 and has a rudimentary web interface. Matters are not so promising if you want to download the dictionary for offline use. The sourceforge page for the mac port seems to be dead, although you can still get version 2.0 of the mac port from the Internet Archive. The Windows port is similarly mired at version 2.1.
The user is instead invited to build 3.0 himself for mac or unix systems. This is something I would attempt if I had the time, but I’ll have to stick to the web versions for now.