Khan AcademyThe Khan Academy is a free Web site that currently features more than 1,600 short (10-20 minutes) videos that teach a variety of subjects, especially in math and science. Users may browse by topic using the headings Math, Science, Humanities and Other, Test Prep, and Talks and Interviews. Louisiana-born creator Khan, a former Silicon Valley investment manager with an MBA from Harvard, hopes that Khan Academy will enable a free “world-class education.”