Probably the easiest Micro-Volunteering opportunity out there, freerice.com
asks you to answer basic vocabulary and grammar questions. For each question right, they donate 10 grains of rice.
Click on the right answer in the middle of this page.
If you get it right, you get a harder question. If you get it wrong, you get an easier question.
For each answer you get right, we donate 10 grains of rice to the United Nations World Food Program.