Words are powerful, and writers have to choose them carefully. Expresso helps improve your writing by analysing your text, pointing out style issues and suggesting alternatives. You simply copy and paste (or type) your text directly into the webapp, hit analyse and you'll get a breakdown of filler words, passive voice statements and weak verbs. Hover over any word and you'll also get synonym suggestions.
Of course, you should use your own discretion when editing (as they point out, writing is an art, not a science), but the tool does an excellent job of telling you where to look. Try it at the link below.