Here's a worthwhile cause, freerice.com and a vocabulary game you might like to try out on yourself.
For every word you get right, the site donates 10 grains of rice to the starving in the Third World, via the United Nations, paid for by advertising on the site. On Novemeber 21, 3,256,135,000 grains have so far been donated.
I'd suggest that the vocabulary is probably going to be too difficult for most of the learners you teach and (from their point of view) it isn't exactly very high frequency stuff, either.
But you might try it out with a Proficiency class — but it really is that sort of level. It might also be a starting point for a discussion…