https://xkcd.com/simplewriter/ 

On this website, Simple Writer your writing is restricted to the top 1,000 most common words in the English language. Every word that is not listed within that database is marked red.

This web app could increase language output by letting students realize that you can say anything you want even by using simple words. So, expressing yourself does not exactly need to tackle the hurdle of learning new and complicated vocabulary.

A task could be that your students have to write about their favorite movie, but they must not mention the title by using only the most common 1,000 words. After that, they read it out and the other participants have to guess the film.