And here I thought every mass market retailer’s app would prove as useless as Zara’s iPhone fail a few months back.

Gap has just released an app that actually does something! It’s on Facebook, and you should consider clicking on over, just to play around with it. For reference, though, here’s a series of screengrabs to feast your eyes on, and to illustrate the actual functionality of the app:

Step 1: Open up the App in Facebook

Step 2: Choose whether you want to play dress up with the lady or the fella. I went with the guy (being one myself)

Step 3: Change your shirt

Step 4: Change your jeans

Step 5: Click on through and go shopping

So why am I loving this? Because it’s SMART. And we like smart. It’s smart to have an app that doesn’t just show the clothing, but allows you to piece together outfits. And it’s really smart to actually allow this app to link through to an online retail experience that’s tailored to the offerings in the app.  The “shop” links don’t go right to the Gap.com homepage. Instead, they take the user to a specific landing page that mimics the look and feel of the app, with tops and bottoms from the 1969 denim collection paired on screen, and available for purchase (separately, of course).

And finally, it’s smart to turn a social media outlet like Facebook into the home of an application. Social networks are all about interaction, and this app enforces that point. Gap allows the user to drive the experience, rather than dictating from the top down.  It’s interesting that the Gap chose to call this app “Lookbook,” because usually a fashion lookbook is professionally styled and immutable. This application is curated and styled, yes, but ultimately, the final outfit pairings are left to the control of each user.

Using an overwhelmingly interactive platform like Facebook to reach out to current and potential customers with an interactive application? Good call, Gap.

Oh, and speaking of interactivity: There’s a “share” feature on the app that allows the user to pass the app along to his or her Facebook friends as a Newsfeed item. This is nothing new on Facebook, but still…clever.

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