Reddit AutoModerator

AutoModerator is a rule engine every subreddit gets for free. Moderators write rules in YAML that match on titles, bodies, authors, domains, account age, karma and more, and then act: remove, filter to the mod queue, flair, comment, report, or ban. It runs on every post and comment before or shortly after it appears.

It's powerful because it's simple and shared. Most subreddits copy and adapt rules from each other. The limits are that it's keyword and metadata based, and only works on Reddit.