Hacker News (HN) is a link-sharing and discussion website owned and funded by Y Combinator, a startup investor; the HN team is editorially independent. Users submit links or text posts, other users upvote them and comment, and the front page lists the highest-ranked stories. Its guidelines say that on-topic means anything that good hackers would find interesting.
Ranking is done by an algorithm: the points of a story are divided by a power of the time since it was submitted, so new stories with votes rise and older ones fall. User flags, anti-abuse software and moderators also change the rank. Show HN is a section for something the poster made that other people can try out; the title begins with "Show HN", and the post moves to the show page after it passes a small points threshold. Asking others to upvote or comment is not allowed and can lead to a ban.
Posting is free. Hacker News publishes its data through a public API on GitHub.