EDIT4:
Bah, it's not free on HostGator even with a free certificate:
_Do you authorize the $2 / month or $24 / year dedicated IP charge? (Dedicated IP required for SSL) *_
_Do you authorize the $10.00 SSL Installation fee?_
EDIT3:
Re: having to buy a SSL on a hobby site / forum ...
Ok I see HostGator allows third party SSL it's not super straightforward but at least it seems possible to use a free SSL from Let's Encrypt and then get it installed...
I have shell access too, but it's not "administrative" access so afaik, the Let's Encrypt "Certbot" would not work?
Would https://gethttpsforfree.com/ work on HostGator with a shared shell access (not administrative), anybody knows?