Both Gizmo and I have https setup on a few of our forums for quite some time. Gizmo is running one of his forums through cloudflair's https system (as posted above) and I am running one of mine through a cert installed on my server.

One of Gizmo's forums:
https://www.agardenersforum.com/forum/
One of mine:
https://www.celicahobby.com/

Beware though, these are live forums, so if you are posting off topic random things to either of the forums, one of the mods may delete the posts or take action on your account

Current developer of UBB.threads PHP Forum Software
Current Release: UBBT 7.7.5 // Preview: UBBT 8.0.0
isaac @ id242.com // my forum @ CelicaHobby.com