I've been playing at Freerice.com lately, during my lunch break.
Every writer needs a spectacular vocabulary in order to choose exactly the right word. Freerice.com is a vocabulary building game. You're given a word and have to choose among three possible definitions, some of which are the less common usage. It's great for SAT prep, but also great for writers.
There's an added bonus. Everytime you get a word right, the site donates ten grains of rice to the United Nations to feed the hungry. Ten grains may not seem like much, but combined with the grains earned by all the other word-hungry people on the site, it makes a difference. Yesterday, those of us who learned between turkey helpings donated 147,385,350 grains of rice. You can check their history to see how much has been donated altogether.
I find the combination very addictive. I like learning new words and I like feeding the hungry. As I watch the grains of rice fill my "bowl" and see the running total, I feel good, which of course, motivates me to play a little longer, but also to try to remember the words I miss so I'll get them right next time.
The game learns your abilities as you play, although it doesn't save from game to game. It gives you some test words to choose your level. If you miss several words, it slides you down. If you get several right, it slides you up. The goal is to make you keep learning without getting frustrated.
There are 100 levels, but I read few people make it past 50. I keep hovering around 40, up a little, down a little. I am going to make it to that magic 50.