RSS/ATOM Feeds
RSS was the first iteration and is therefore widely adopted. ATOM tried to improve on RSS in various ways like having an official RFC. This website serves both RSS and ATOM because I'm using a nifty Python library called feedgenerator which can generate them both.
Feeds go in and out of popularity - there's a long running joke on the internet that feeds are dead. The reason for some folks wanting it to die off is that feeds generate a lot of internet traffic: feed readers have to constantly be polling the feed for updates and 99% of the time there won't be an update.
My Favorite Feed Readers
My Favorite Feeds
Some of my favorite feeds are:
Feed Validation
There are various feed validators out there on the web. Here's one that shows this website's feed is valid: W3C.
Search Results As a Feed
Search results from a search engine make for a great feed. See the OpenSearch protocol as an example.
If This Then That
This is another nifty usage of RSS feeds: any time there's a new item in the feed it triggers an action on another service or device.