The United States Department of State's Bureau of Educational and Cultural Affairs offers free MOOC courses for ESL Learners.  See the listing below.  (Note that some are for teachers of ESL, some are for Learners of ESL).

• Current Massive Open Online Courses (MOOCs)
• Upcoming Massive Open Online Courses (MOOCs)

Courses useful for ESL students include:

• English for Career Development (Self-Paced)
• English for Science, Technology, Engineering and Mathematics (STEM) (Self-Paced)
• English for Journalism (Self-Paced)
• English for Business and Entrepreneurship (Self-Paced)
• English for Media Literacy (Self-Paced)