I'm familiar with three, but they're new or sparsely populated (which may be what you're looking for).

LamerNews http://lamernews.com/ - Created by antirez to showcase a forum backed entirely by Redis.

Lobste.rs https://lobste.rs/ Created by jcs after he was hellbanned from HN

Monocle.io http://monocle.io Created by alex maccaw very recently.