Fototwics (free) is a photo sharing app that joins a crowded field with offerings from titans like Apple, Facebook and Instagram.
The difference is that Fototwics is not a filter or photo altering app, but just a way to share your photos privately or publicly. For public sharing you can add hashtags, and also use the tags to see photos that may appeal to you. Essentially, Fototwics is a photo blogging app that gives you some of the features of Apple's PhotoStream, and some of the photo sharing features of Instagram. The Fototwics designers were aiming for something different from Instagram though, as it dispenses with likes and dislikes and lets your photos be shared with groups or individuals who then re-share or "re-twic" the photo to others. Fototwic is trying to break open the closed sharing model of Apple and Instagram, and it seems to accomplish that.
Fototwic requires a free signup that generates a user name for you. As soon as you're signed up, you can post publicly or privately while you generate followers.
Photos can't be modified other than cropping and rotating, but there is nothing that stops you from posting a photo you have edited in another app, including Instagram of course. Your images can be shared via Facebook, Twitter, Instagram, Tumblr and Flickr with a single click. Other Fototwic users can leave comments on your pictures, and you can do likewise to other photos.