Millions of students have signed up for massive open online courses, and hundreds of universities are offering some form of Web-based curriculum. Most students aren’t paying much for these classes, if they’re paying anything at all. So where is all that knowledge—and all the cash—coming from?

Coursera

Khan Academy

Udacity

edX

This for-profit MOOC founded by Andrew Ng and Daphne Koller has teamed up with 62 colleges (and counting) for its classes. The company is experimenting with a career service that makes money by connecting employers to its students, and attracted $22-million in venture capital in its first year.
Salman Khan made waves when he quit his job as a hedge-fund analyst to record short video lectures on everything from embryonic stem cells to—you guessed it—hedge funds and venture capital.
This for-profit MOOC, started by the Stanford professor Sebastian Thrun, works with individual professors to offer courses. By March 2013, Udacity had raised more than $21-million in venture capital.
Harvard and MIT put up the original $60-million to start this nonprofit MOOC. So far, students can take classes only from Harvard, MIT, and UC Berkeley, but classes from nine more universities are coming soon.

Companies to watch:

MOOC2Degree: This upstart’s main selling point is real, transferable credit, as long as students can get admitted to the college, that is. At least nine colleges are planning to participate, and Jeb Bush, the former Florida governor, has spoken favorably of the venture.
Canvas Network: Network's owner, Instructure, is one of Blackboard’s biggest competitors. David Wiley, an early MOOC teacher and promoter, has gotten behind the project, and more than a dozen colleges have signed up. The company has received more than $9-million in investments.
CourseSites: Blackboard is only just starting to compete in the MOOC universe with its CourseSite platform. So far, only a handful of universities have tested it out.
Udemy: Professors, authors, professionals, and celebrities create and sell courses about pretty much anything at Udemy, which has raised more than $16-million in venture capital.
Thinkful: One of the billionaire Peter Thiel’s 20 Under 20 fellows started this career-development-oriented company, into which Mr. Thiel has invested $1-million.
Graphic by XARISSA HOLDAWAY; illustration by NIGEL HAWTIN
Sources: THE CHRONICLE OF HIGHER EDUCATION, FINANCIAL TIMES, NATIONAL SCIENCE FOUNDATION, THE NEW YORK TIMES, TECHCRUNCH, CNN, WIRED, AND YAHOO FINANCE