Vienna is an open source Mac OS X RSS reader with support for RSS/Atom feeds.

Vienna emphasizes a simple interface over a large feature set.

Vienna's features include:

Support for Atom/RSS news feeds and podcasts.

Built-in tabbed web browser using WebKit.

Smart folders, similar to the smart folders offered in Apple's Mail application, for organizing related articles.

Selectable and customizable styles via HTML templates and CSS.

Full AppleScript support.

User notification via Growl.

Vienna is coded in Objective-C using Cocoa. It uses SQLite for data storage.