MG Mason, in his wonderful blog Sweat, Tears and Digital Ink, has compiled a great list of resources.

Writing & Language Tools

1. Blabla meter for when you really need to be told that there’s too much waffle in your writing
2. FreeMind: a brainstorming tool
3. English Stack Exchange. A very nerdy linguistics resource
4. Evernote: A cloud application that makes for a good tool for storing and sharing research and notes across multiple devices
5. Onomatopoeia dictionary Ta-dah! needs no explanation
6. Oxford Dictionaries British-American English Comparison. Want to know your pavement from your sidewalk or your aubergine from your eggplant? And what is a courgette anyway?
7. Synonym Finder (and antonyms) for all of your word finding needs
8. VisuWords is a clever dictionary/thesaurus/wordfinder/word association tool that uses a graphical interface
9. Wordnik: An encyclopaedia of words. Antonyms, synonyms, etymology, demonstrated use. Create lists of your favourites
10. Write or Die: Creative writing sadism with punishment for not keeping up

Writing prompts

1. Creative Writing Prompts. Some simple ideas to get you started
2. With Painted Words: Picture prompt. Earn money too!

eBooks

Edited by Zoe

Other

1. Book Crossing: Give a book away but first put a label on containing a unique code from this website. Then watch it travel the world.
2. Rare Book Room: HQ digital photographs of some of the rarest books on the planet. Examine them without having to visit the national library in another country and more importantly, without damaging them
3. Read It Swap It: Have lots of books in storage that you don’t want to give away, can’t sell and will never likely read again? How about swapping it for another book? Simple premise and it works. I’ve acquired three books through this site already.
4. Librivox: Download free audiobooks voiced by volunteers. Or perhaps you might want to volunteer yourself

Check his blog at:

Sweat, Tears and Digital Ink