There's both an Android app and an iOS app for FxCamera, and both are great. It lets you add many different effects to your photos, such as Fisheye, toy camera, vintage, and many others. Especially nifty is that you can also record a voice message to go along with the photo. And you can share it all on Facebook and Twitter.
This app, which comes both for Android and for iOS is a superb photo editor, with many powerful editing tools, and plenty of special effects, as well as the ability to add frames. Snapseed was bought by Google a while back, so it's no surprise that it lets you share photos via Google+.
This great app for iOS lets you take 360-degree photospheres, and then share them with others. Don't be put off if when you first put the photosphere together you think you've done something wrong, because it gets uploaded to the cloud, where it gets stiched together properly.
Here's and Android app for taking photographs with eight different photo shooting modes, plenty of effects, and letting you share your photos on Facebook, Twitter, and other places as well.