I’d say quite minimal… In appearance? 
- 5-6 most used categories, a few other niches
- scarce nested categories, not for main categories
- 2 tags reserved for a single category
Chat enabled for direct messages only, but it’s barely used (except by staff)- 1 theme
- very few tweaks (two custom badges, css, 1 group for professionals)
- 2 official plugins:
- 3 third-party plugins:
- A few third-party and official components:
- Emoji Fluff
- MD Topic List Mobile component (can’t stand the defaut mobile topic list view)
- Inline PDF Previews
- Versatile Banner aimed at greeting visitors and new members, but I should work on it
- Progress Bar activated only when we’re on the community donation goal to pay the servers
- + a few tiny other ones not necessarily worth listing
- Thinking of using LLMs to fight spam as all alternatives I tried are not perfect enough after all
Topic GalleryVisually speaking, and when it is used as an admin or user, the forum looks and feels mostly like a default install, with slight new features and tweaks.
I think that a strong force of Discourse is to be very capable in terms of features as a default install, while still providing a vast array of official, maintained plugins.
And I firmly believe many instances can work very well without or with very few modifications.
Remember, folks: each time you add an official, third-party, or custom modification to your site, you also add a potential point of failure!