RSS.app for Mac Menu bar app that uses Notification Center to update you.
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RSS.app for Mac Description

RSS.app is the ideal tool for the casual RSS user. The app is almost invisible: It is embedded in the status menu and uses Mountain Lion's Notification Center to alert you of new posts. You can use RSS.app to import your existing list of RSS feeds from Apple Mail -- even after you've updated to Mountain Lion. Or import them from Google Reader. It's like having native RSS functionality built into the operating system (again)!

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