silos that have a "mute" feature for hiding posts from people so you don't have to see what they post, without having to unfollow them.
Flickr - added in 2007?
Facebook - added in 2010?
Flaminga was (site went down ~2014-12) an in-development Twitter client that proposes some elegant solutions to spam and abuse on Twitter.
- Shared mute lists. Subscribe to a friend's mute list
- Mute tweets from a muted user's followers
- Mute tweets that mention you along with a muted third party
- Mute brand new users (configurable 1 day to 1 year)
- Mute users who post too many repeated links, or who are muted by others