Windows/Mac/Android: Carbonite Currents keeps track of the documents you open and work with, and gives you access to all of them on any device. If you work on a file and forget to put it in your Dropbox folder or email it to yourself, Currents shows it to you. It's a handy service, and it's completely free.
The video above does a good job of describing Currents, which is Carbonite's first non-backup related product. Install the free app on any device you work with. As you work, the files you access will float to the top of your Currents list. You can select the folders on your computer you want Currents to keep an eye on for changes. You can even select items from your mobile device for Currents to watch, such as your camera roll, music or movies. By default, the app will keep 30 days of revision history and file/folder changes, so you don't have to worry about accidentally deleting something or overwriting a file you meant to open or change.
Once installed, Currents shows you all of your most recently changed or created files across all of your devices and folders. You can open them directly from Currents and work with them immediately. You can share files with others, view or add comments to the files, or view the revision history on any device.
Carbonite positions Currents as a Dropbox competitor. We don't see it that way: Currents is a useful addition to a cloud storage service, not a replacement. You can even tell Currents to monitor your Dropbox folder. You don't have to manage another cloud service, or deal with storage quotas or issues -- it's simply an easy way to get access to and organise the files you work with most often.
The service is in public beta, and its Android app is live at Google Play. An iOS app is expected soon.
I encountered a few bugs here and there (such files that are slow to load or appear in Currents, and a very non-tablet optimised Android UI). Nonetheless, the service performed pretty well and worked as advertised. I could easily see and open files I worked with on my Windows and Mac desktops using my Android phone. The beta is completely free, though Carbonite is planning a premium service in the future that will let you track longer than 30 days of revision history.