Instagram is an iPhone app that not only lets you add cool, old-school effects to any photo but also makes it a breeze to share them on your social networks.

It’s quite simple. Tap on “Share” and the app will launch your iPhone camera. Snap your shot and the app gives you a whole range of effects for you to choose to give your photo an old-school feel – think Polaroids. Add a caption and you’re ready to share the pic with the whole world on Twitter, Flickr, Tumblr, Posterous, Facebook and Foursquare with the slide of a button – all at once.

Instagram is, in itself, a social networking app of sorts. Tap on “Feed” and you’ll see not only the photos you’ve shared but also photos from other Instagram users you follow. You can comment on and like their photos and they might just do the same for you.

If your photos get a lot of likes, they might be featured in the “Popular” section.