Did you figure this out yet?
By 'registration' do you mean:
1) A course that is open to people who do not even have an account yet.
2) A course that does not require authenticated users (user with an account) to enroll in it.
You can do this to a certain degree with guest access, but note that participants will only be able to read, watch or listen to materials - they won't be able, for example, to participate in forums or take quizzes. You need to enable guest access - see the documentation Guest access. Enabling the setting 'auto-login guests' is also helpful in that they won't need to click the "log in as guest" button.