Custom Feed Parsers in a Rails App with Feedjira
Note: Just before I started writing this, I noticed that the Feedzirra gem had 1) changed it's name to Feedjira (explanation here) and 2) had pushed a bunch of updates. Everthing I talk about below worked on 0.2.4, and appears to work just fine on 1.2.0. Also, looking at the CHANGELOG, none of the updates should mess with what I talk about here.
Web feeds (RSS, Atom, etc. - but I tend to call them all "RSS feed"), while sometimes viewed as unfashionable/antiquated, are ubiquitous among web publishers. When you are building a system that needs to know when new content is published, RSS feeds are a perfect low-bar method for doing programmatically discovering new content.