Wordnik
Wordnik is the world’s biggest online English dictionary, by number of words. Wordnik shows definitions from multiple sources, so you can see as many different takes on a word’s meaning as possible.
Google Books
In alignment with their corporate mission statement “to organize the world’s information and make it universally accessible and useful”, Google Books boasts the world’s most comprehensive index of full-text books. It also allows users with Google Accounts to create a personal library as is shown in the image for this post (blue text, beneath the search bar). Google Books also allows for the borrowing of certain books.
Language Tool
Language tool is a nifty website for checking the grammar of text passages under 20,000 words. In the free version, the website states that it has thousands of patterns it uses for finding errors. It also exists as an add-on for Google Docs.
Lexipedia – Where Words Have Meaning
Lexipedia is an online visual semantic network with dictionary and thesaurus reference site. Lexipedia presents words with their semantic relationships displayed in an animated visual word web.