I am just on a roll this month! Here's a stupid-simple Sinatra app I created for my wedding attendees. Weddings generate a lot of pictures. An insane amount of pictures. I needed a fast, easy way for attendees to upload their pictures to my Amazon S3 bucket without too much technical know-how. While Facebook and Google+ are really nice for sharing photos, I wanted the originals, in their original forms, without any added compression or tinkering.
Enter DeadDrop, a simple upload web app that works with the local filesystem or Amazon S3. This app accepts uploads of any file type by default, of any size, of any number (these things can be limited, check out blueimp's documentation on how to make this happen). Drag and drop support as well as a fallback form is included.
The app doesn't give out or support links to uploaded files, so it isn't really appropriate for a file locker service at the moment. If you'd like to make this happen, send me a pull request.