Pileup let you sort your vast camera roll (or any other photo source, including a cloud folder) in a freeform way. It mimicked the way people used to sort physical photos -- making little piles.
Rather than a traditional file explorer, where creating a new folder means naming it, with Pileup you just flick a photo into one corner of the screen and name it later ("Freshman Year").
You're presented with one photo at a time in the center stack. Double tap on a photo to send it to the back of the stack and come back to it later.
Pull a photo to the bottom of the screen and a trashcan will meet you halfway to delete it.
Flick from a corner toward the middle of the screen to undo the last photo you sent there (honestly, I think this is incredible -- it's an unlimited undo that isn't linear. I want every app to add that).
Tap a pile to select it and share, rename, delete, or sort within it.
The teal bar at the top gets smaller with each image you sort, indicating your progress toward organization enlightenment.
Who knew Windows' folder interface was so bad? I designed my own from scratch, with nested folders, and horizontally scrolling thumbnail previews so you could peek into a folder before deciding if it needed sorting.
See more about this project here.