Advanced English & Thesaurus This thesaurus will help you find just the word you're looking for. It's pretty intuitive in its suggestions, and it also works totally off-line while taking up very little space on your phone.

Evernote This is a super app that's great for everyone. But I also love it for authors. Is there anything more frustrating than having inspiration strike, only to forget your idea before you get it down on paper? Well, with evernote, that won't happen anymore. Also, if you see something that inspires you, you can take a snapshot and store it right then and there!

Oxford Grammar and Punctuation This is the electronic version of the grammar manual I used as a student, and I find the app is still helpful in answering some of my grammar related questions