I found some threads that touched on this, but they were 5+ years old and there weren't any firm outcomes that I identified.
In reply to Brian Reinicke
Re: A class that can start anytime and completed leisurely
by Richard Oelmann -
Publicise those courses on the front page or somewhere - there are a few themes that have options for 'promoted' courses, marketing spots or similar - or simply create a 'glossary' to use as a course catalogue.
Then on the courses, enable 'self-enrolment' and the users can enrol themselves as and when they want to.