Aircosm is a Usenet-inspired discussion platform. Groups work like tags in a dot-separated hierarchy, posts can live in several groups at once, and you move through your unread posts in a focused, swipeable feed. Read a post once and it stays read everywhere.
A single post can be tagged into many hierarchies like comp.lang.python without duplicating content.
Scroll or swipe through unread posts in chronological order. Scrolling past a post marks it read across every group.
Replies keep their parent available in a collapsed header, so a conversation never loses its thread.
Reading is open to everyone. You only need an account to post, reply, or vote.