It all started with stanford professor Andrew Ng announcing his class free of cost to students all over the world - Machine Learning.
Coursera: Andrew Ng and Daphne Koller from Stanford University
Udacity: Sebastian Thrun, David Stevans, and Mike Sokolsky
Edx: Massachusetts Institute of Technology and Harvard University
Though started as MITx, by MIT the project later maerged to form Edx.