Old Reddit, with limited/selected subReddits, no thumbnails.
One that I'm working on myself and too afraid to post publicly. The people on this site are not my target audience either.
ps. There's no one on it but me.
Probably one of my own communities. Hell, maybe I'd set up that universe's equivalent of Hacker News or something, rather than it being a Ycombinator project.
subreddits with strong moderation are indistinguishable from hn
also indiehackers.com
/. for old trolls reddit to ctach up new ones
lobste.rs
Reddit, lobsters, some of the HN clones also get a bit of traffic so I might aggregate them somehow.
I like reddit because you join the ones that gel with your tolerance of sillyness. I like a bit of humour but not a chain of 100 replies to a fart joke.