Built-in motivation for vocab review
FreeRice is pretty simple. There are a number of topics (humanities, science, math, language, vocab, etc.) and a series of flashcard-style questions for students to work through.
As students answer questions correctly and move through the series of "cards," they earn charitable contributions of rice to individuals in need around the globe.
As can be expected, this World Food Programme site has some built-in motivation. Students are drawn to the concept of giving and are quick to get sucked into quizzing themselves on vocabulary, math, language, etc.
How I Use It
As other users have pointed out, there's not a lot of customization for specific needs, questions, etc. It's just random questions, multiple choice answers.
Having said that, I do think there's value in an engaging program that gets students excited about working their way through random questions like these. It's definitely not the most effective way to learn or retain info, but it certainly exposes students to words, concepts, and questions that will benefit them in the long run.
In my classroom, Freerice is used only as filler--those occasional last 5 minutes left in class, as students are finishing up a quiz etc., when one group completes a task much quicker than the others...There's no points, no assignment...just log on and see how much you can donate when the appropriate time arises (which really, isn't that often).
Students usually jump at the opportunity to see how they can do.