Mobysaurus Thesaurus

if you write a lot of essays and your vocabulary skills (like myself) just isn't up to par, then a desktop application such as Mobysaurus Thesaurus would definitely help you out.

These types of tools are not only great for writing, but it expands your vocabulary, and allows you to craft better writing. Seeing how this is free and donationware for Windows, there's not really any reason that you shouldn't get it. I would probably also recommend this those that are in school since there is a lot more opportunity to increase your writing skills.