You wouldn't expect such a great app to be free to download and use, but it is. Ziibii  brings together all your favorite social services (Facebook, Twitter, Flickr, and YouTube), and puts your friends' updates on a flowing river on your iPhone / iPod touch.

“Enjoy a fresh, new way of staying in-touch and in-the-loop with your friends, photos, and the world around you with Ziibii!,” says the Zumobi Network.

“Ziibii blends Facebook, Twitter, Flickr, and YouTube - plus your favorite web content - to deliver an iPhone experience unlike any other. Ziibii is easy-to-use, fun to explore, and offers plenty of great features ... Download Ziibii now, and start enjoying your river of friends, photos, and feeds! ... Your friends don’t have Ziibii yet? No problem – send ‘em an email with any Ziibii item and they’ll get a link to the App Store, so they can enjoy Ziibii, too.”

According to the makers of the app, you can customize Ziibii with a virtually unlimited selection of web content (via RSS feeds), with just a few taps. The UI is as pleasant as it is flexible, and if you want to see more about a headline that’s floating by, simply tap it to open up a preview of it. Another tap takes you to the full story and website.

Photos, too, open with just a tap as “Ziibii works hand-in-hand with Twitter and email,” according to Zumobi. Share, or comment on Ziibii content with your Twitter followers, or via email, the possibilities are endless.

So, while Twitter, Facebook, Flickr, and YouTube are featured by default, you are also able to add presets from Ziibii's list of popular sites, or add your own favorites. However, an option to post updates and photos to Twitter, Facebook, and Flickr would have really set users on fire, TUAW suggests. Should the folks at  Zumobi Inc. be listening, future updates may very well include these features, as well as support for Pownce and Digg.

Download Ziibii via iTunes App Store (Free)