Hacker News employs the reddit technology for displaying popular stories/news items. Reddit is one of the companies Paul Graham‘s Y Combinator project helped seed-fund a few years back.
The concept is somewhat similar to Digg, but without needing a ‘DiggIt’ button on a website to add it to the reddit list – you just submit items directly to reddit like sharing a link on Facebook.
It moves in popularity by user votes, somewhat akin to the ‘Like’ button on Facebook – but can be downvoted as well.