Mac: Dropbox is excellent for keeping your files in sync across devices, but if you ever forget to put a file into your Dropbox folder, you're pretty much out of luck. Spotdox is an app that runs on your Mac and gives you remote access to any file on your computer through your Dropbox account.
With Spotdox running on your Mac, you can remotely access any file on your computer from either a mobile device or a computer. Just head to the Spotdox website, log in, and you'll see all the files on your computer. When you find the file you're looking for, Spotdox transfers it into your Dropbox account so you can access it right away. It's certainly not something you'll need to use very often, but it's a dead-simple way to make your computer easy to access from anywhere without really setting anything up. Currently, Spotdox is free for the first 10,000 users.