Private companies, like Phoenix, have been offering online degrees for a fee for years. And schools like M.I.T. and Stanford have been offering lectures for free online. Coursera is the next step: building an interactive platform that will allow the best schools in the world to not only offer a wide range of free course lectures online, but also a system of testing, grading, student-to-student help and awarding certificates of completion of a course for under $100. (Sounds like a good deal. Tuition at the real-life Stanford is over $40,000 a year.) Coursera is starting with 40 courses online — from computing to the humanities — offered by professors from Stanford, Princeton, Michigan and the University of Pennsylvania…

In each course, students post questions in an online forum for all to see and then vote questions and answers up and down. “So the most helpful questions bubble to the top and the bad ones get voted down,” Ng said. “With 100,000 students, you can log every single question. It is a huge data mine.” Also, if a student has a question about that day’s lecture and it’s morning in Cairo but 3 a.m. at Stanford, no problem. “There is always someone up somewhere to answer your question” after you post it, he said. The median response time is 22 minutes.

These top-quality learning platforms could enable budget-strained community colleges in America to “flip” their classrooms. That is, download the world’s best lecturers on any subject and let their own professors concentrate on working face-to-face with students.