Vienna

Vienna is a open-source feed reader that lets you follow the latest events from the websites you're subscribed to. It's capable or interpreting RSS and ATOM channel formats.

It has three different ways of presenting the information, although in all of them the channels always appear on the left.

The righthand side is reserved for articles. You can sort them using a variety of fields (read, theme, folder, file, author, etc.), apply more than a dozen templates to format your content, and increase or decrease the font size to make them easier to read.

Another of of Vienna's interesting features is its tab system. When you open an article's external link, it will show up in a new tab within the program interface. It uses the Safari browser to do this.

Lastly, Vienna lets you create intelligent folders, or in other words, folders that filter content dynamically according to the criteria defined by users. It's also compatible with AppleScript.