Not exactly sure what your requirements are but vanilla forums have a clean look, mobile friendly, and have pretty good customization.
(Not sure if the latest version supports digest emails though)
This might not be what you're talking about, but there seems to be a bit of a throw-back theme in the repo. Not the one I remember from when I last looked at Vanilla Forums, but certainly reminiscent of it.
"The master branch is considered a stable branch capable of being released at any time. Reviewed, stable changes land against master via pull-request."
Last update was jul 13.
It's pretty stable and has been around for a while, so i wouldn't expect a flurry of constant changes (durability and stability are exactly what i look for when self hosting)
https://github.com/vanilla/vanilla