A summary mashup from the FAQ:
EdX is an enterprise of MIT and Harvard University. EdX is building an open-source online learning platform and web portal for online learning; HarvardX, MITx and BerkeleyX currently offer classes online for free.
learners who demonstrate mastery of subjects can earn a certificate of completion. Certificates will be issued by edX under the name of the underlying "X University" from where the course originated, i.e. HarvardX,MITx or BerkeleyX. For the courses in Fall 2012, those certificates will be free. There is a plan to charge a modest fee for certificates in the future.
I'm signed up for 6.002x, Circuits and Electronics from MITx and CS169.1x, Software as a Service from BerkeleyX.

169.1x starts Sept 24 and ends Oct 26th, with an estimated required effort of 12 hours a week. Course staff is Armando Fox and David Patterson. CS169.1x teaches the fundamentals for engineering long–lasting software using highly–productive Agile techniques to develop Software as a Service (SaaS) using Ruby on Rails.
Todd Hopkinson