Sample image of Currents Producer. Courtesy Google Mobile blog

Thursday, Google finally launched its long-rumored magazine-style publishing platform for tablets and smartphones. It’s called Currents, and it’s available now in the U.S. for both Android and iOS.

In development, it was code-named Propeller. It’s been percolating for most of 2011. Rumors placed it anywhere from a brand-new tablet-first UI for Google Reader to a Flipboard-style social news filtering and recommendation service.

It turns out that while Currents contains pieces of all of those, it’s probably thought best primarily as a platform for established and independent publishers to quickly develop magazine-style touchscreen layouts for news stories and other content.

“We felt there was an amazing amount of great online content that was not being displayed well when we tried to access it on our phones and tablets,” Google’s Mussie Shore told Andrea Spiegel at Forbes. “We personally knew many creatives who were frustrated at the gap between what they envisioned for their content on tablets and phones, and having the right tools to deliver their vision. Google is attracted to these type of ecosystem opportunities.”

Think of it like Blogger and Blogspot — just for the age of tablets and smartphones.

Google is launching with more than 150 partners, including newspapers, magazines and blogs, each of which is producing one or more “editions” for Currents. As a reader, this is your first stop to customize content within the app.

In addition to Editions, Currents’ content is rounded out by trending topics sorted by category from Google News, RSS feeds, public Google+ streams and Google Reader subscriptions. It handles video and photo feeds and content as well as (or better than) text. Sharing to email, Facebook, Twitter, Tumblr, Instapaper, and Pinboard is built-in, as well as integration with Google+.

There’s also a Google Currents “Producer” that in principle allows independent publishers to create and distribute their content for the platform, too, on smartphones and tablets for both Google’s Android and Apple’s iOS.

I still don’t know if Google has gleaned what so many of us find valuable in Twitter and Flipboard as social tools for news discovery. Given its brusque elimination of the built-in social features within Google Reader itself, I don’t think they do.

So don’t call Google Currents a social news reader. It isn’t one, really. What it is, however, is a very slick way to get content onto touchscreens across platforms in a hurry. That’s impressive enough on its own.