Google Reader, launched in 2005, is an aggregator for web feeds. The browser-based reader lets users add RSS and Atom feeds and search for them too. The service will be discontinued on July 1, 2013. However, some companies are offering free alternatives that work with your Google Reader subscriptions.
The reader gives you a "reading list" that shows which items you've not read yet. You can sort items in this by relevance as well as date.
Like Gmail, you can apply labels and stars to your subscriptions.
The reader has a number of keyboard shortcuts, many of which are the same as those used in Gmail, making the application easy to use if you're already familiar with Gmail.