Simple Update Protocol

Simple Update Protocol, or SUP, was a protocol developed by FriendFeed to simplify and speed up RSS and Atom.wikipedia
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FriendFeed

Simple Update Protocol, or SUP, was a protocol developed by FriendFeed to simplify and speed up RSS and Atom.
Employees of FriendFeed created the Simple Update Protocol to reduce the load put on sites by aggregators such as theirs.

RSS

RSS feedsRSS feedReally Simple Syndication
Simple Update Protocol, or SUP, was a protocol developed by FriendFeed to simplify and speed up RSS and Atom.

Atom (Web standard)

AtomAtom Publishing ProtocolAtom Syndication Format and Atom Publishing Protocol
Simple Update Protocol, or SUP, was a protocol developed by FriendFeed to simplify and speed up RSS and Atom.

Reddit

subredditReddit AMAAMA
A few websites supported SUP for a while, meaning that updates from their services appeared in FriendFeed within seconds, until support was dropped, and eventually FriendFeed itself shutdown 2015-04-09. These sites include Disqus, Identi.ca, reddit.