A great list from Zoe at Just English.
1. Words-to-Use.com — A different kind of thesaurus.
2. OneLook.com — One quick dictionary search tool.
3. Vocabulary.com — The quickest, most intelligent way to improve your vocabulary.
4. ZenPen.io — A minimalist writing zone where you can block out all distractions.
5. 750words.com — Write three new pages every day.
6. Readability-Score.com — Get scored on your writing’s readability.
7. YouShouldWrite.com — Get a new writing prompt every time you visit.
8. WriterKata.com — Improve your writing with repetitive exercises.
9. IWL.me — A tool that analyzes your writing and tells you which famous authors you most write like.
10. HemingwayApp.com — Simplify your writing.
11. FakeNameGenerator.com — Generate fake names for your characters.
12. Storyline.io — Collaborate on a story with others by submitting a paragraph.