Is it possible to make parts of a course visible to the public (not enrolled in the course) while at the same time keeping other parts of the course hidden from the non-registered public? I'd like to make the wiki or blog section 'public'- so that we can share our discussions with non-enrolled people- but at the same time keep the rest of the course only available to enrolled students.
My first answer: No, AFAIK, either Guest Access is set, in which case guests can enter and see courses or they cannot.
My second answer: Maybe... in fact quite possible, with judicious use of course permissions overrides. But you need be very careful here as it might have an effect outside of a course.
In the course, allow Guest Access, and for all activities you do not want them to view, set them to Hidden. For all Students in the course, go into Permissions overrides and set the capability to "View Hidden Sections" to Allow Students. (Your theme will determine how this is set up but in mine there are two buttons, one to allow things and one to disallow things, may be the same for you.) For this, you will have to make sure that the things you want the Guests to see are in separate sections, and I haven't checked any further than that. There may be some refinement that allows you to keep sections visible and just hide resources and activities, and a permission to allows students to view hidden resources and activities, but I didn't look.
I suggest that you can ONLY do this in a course and need to set it up for each course you want this to happen on. Anyway, that is the best I can think of...