Here’s our forum!:
We’re using a pretty vanilla install, i.e. not really any plugins beyond the WP Discourse plugin for SSO with our Wordpress site. But we’ve done some fairly extensive frontend / design tweaks.
Aside from color scheme and some UI adjustments and simplifications I think the most noticeable thing we did is add a visual header banner for each category. We liked how this looked on some other sites we came across e.g. Flarum and found it nice to have extra visual distinction for categories. This is done with custom HTML in the “after header” section plus some fairly complicated CSS targeting…luckily Discourse has category slugs included in class names!
Other tweaks we did include a custom header (won’t go into detail b/c there are other great detailed tutorials on that to be found here!); a bunch of minor things w/ text size and button display; and hiding a few things with “display: none” that seemed inessential for our moderately sized forum, to try to minimize visual clutter.