It's so popular, that I did not want install it on my phone. I have nothing against Instagram, but if you're one of those who want to try other creative apps, do check out Snapseed which is also a free app.
Recently acquired by Google, this one-stop photo editing app was released in 2011 and is available for both IOS and Android. Users can easily access the toolbar where effects and edits can be chosen using smart touch gestures to make even deep photo editing possible. It brings out more of the creative modifications rather than pure photography output which users can instantly share through social networks and on other websites.
Other recommended apps:
Free iPhone and iPad Apps: Action Movie FX and Rome MVR
iOS Game Apps: Grand Theft Auto III, Beat Sneak Bandit, and N.O.V.A 3
Free Android and iOS Tablet App for Fashionistas
also published by author on Bubblews