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.
Lingro refers to itself as the coolest dictionary known to hombre.
When you visit the website, you can paste the address of another website into the top search field, then it will allow you to click on words you don’t know the meaning of, and Lingro will define the words.