Grammarly is an automated proofreader – for online use. Download/install it to your laptop or tablet from Grammarly.com and spell check your way through Gmail, Facebook, LinkedIn and Tumblr. It will even proof your Tweets, ensuring you don’t waste a single character! Grammarly checks for spelling (including contextual usage), grammar and punctuation, and provides suggestions for improved vocabulary usage.
Basic service is free. Premium options with additional proofing and editorial features are available through paid (and pricey) subscriptions. Note: the service does not work on smart phones. But where it does work, it is a welcome tool indeed.