RSS is a format for syndicating news and the content of news-like sites, including major news sites like Wired, news-oriented community sites like Slashdot, and personal weblogs. But it's not just for news. Pretty much anything that can be broken down into discrete items can be syndicated via RSS: the "recent changes" page of a wiki, a changelog of CVS checkins, even the revision history of a book. Once information about each item is in RSS format, an RSS-aware program can check the feed for changes and react to the changes in an appropriate way. RSS-aware programs called news aggregators are popular in the weblogging community. Many weblogs make content available in RSS. A news aggregator can help you keep up with all your favorite weblogs by checking their RSS feeds and displaying new items from each of them.
But coders beware. The name "RSS" is an umbrella term for a format that spans several different versions of at least two different (but parallel) formats. The original RSS, version 0.90, was designed by Netscape as a format for building portals of headlines to mainstream news sites. It was deemed overly complex for its goals; a simpler version, 0.91, was proposed and subsequently dropped when Netscape lost interest in the portal-making business. But 0.91 was picked up by another vendor, UserLand Software, which intended to use it as the basis of its weblogging products and other web-based writing software.
In the meantime, a third, non-commercial group split off and designed a new format based on what they perceived as the original guiding principles of RSS 0.90 (before it got simplified into 0.91). This format, which is based on RDF, is called RSS 1.0. But UserLand was not involved in designing this new format, and, as an advocate of simplifying 0.90, it was not happy when RSS 1.0 was announced. Instead of accepting RSS 1.0, UserLand continued to evolve the 0.9x branch, through versions 0.92, 0.93, 0.94, and finally 2.0.
