See RDF Site Summary (RSS) 1.0. See also What is RSS?.
Clients
I haven't found any lightweight (no Gnome, Java, KDE, etc) client under Linux. I tried the irssi script but it doesn't seem to do automatic notification.
I ended up using an RSS to email gateway after tweaking it slightly. I sent my changes to Dean and Aaron.
Note that Max reads his directly from Gnus, which is pretty cool.
For my own work
EmacsWiki support? I have written a prototype: RssForEmacsWiki.