Here is a post from ‘A JOURNEY IN TEFL’ blog.
SKELL is a simple tool that allows students and teachers of English to quickly check if a phrase or word is being used correctly.
It is free. Simply type a word and press the button.
Example sentences, collocations, and synonyms for the word you typed in the search box will appear. The tool will be very handy while your students are writing an article, story etc as it will allow them to see word sketches besides the synonyms and the example sentences.