Split Pic Pro is a fun photo-editing app that lets you clone yourself (in a manner of speaking), create collage-like projects, add effects, then share your work with your friends.
To get started, you need to select one of the 12 different layouts. You have the option to move each of the bars that separates your layout for a little customization, but it really seems like it needs more default layouts. Fortunately, even with the small assortment, you'll be able to make some really cool projects.
The next step is to fill each of the panes with an image and position your photos. You can either snap a fresh photo, use the menu button in the lower left to grab an image from your photo library, or use a timer for self shots. When you have your pictures selected, on the lower left of the interface there's a pointer icon with two settings. When it's orange, you'll be able to move the separators. When you touch it again it turns purple, letting you pinch to zoom and move an image around within each pane.
To add to the effect, the next step is to blur and blend the separators. While you won't always get a perfect blend between the images, I found that some work extremely well, especially if the lighting in each of the images is similar.