Rewordify is a free website that allows you to paste any text or website into an engine that replaces complex words with easier ones. Our Special Education teacher has recommended it for use with students who might be a bit below grade level in their reading skills, but any student or adult could use it to work on their vocabulary or to better navigate required reading.
The Rewordify for School page shows functions and other ways to us the engine in schools. For example:
Beyond Survival in a School Library 
Good grief; I sure could have used this when I was teaching!
I know! Isn’t it cool?