Reviewed in Top 15 Apps
Much like Cloudii, FolderSync lets you access all of your cloud storage services in one app. But it also allows you to set up sync schedules between specific folders on your device and whatever cloud services you like. It can also work as a file manager if you need one.
Reviewed in My Essentials
This app let's you sync specific folders from your various cloud storage accounts (only two accounts in the free version) to specific folders on your device like cloud folders on a PC. This is especially useful for times without an Internet connection as your files are already saved for you. You have complete control over when and where syncing occurs to save battery or data, and syncing can go both ways.
Reviewed in Selig's choice of System tools
[no root required] FolderSync does not necessarily make a "system tool", but I wouldn't want to use a phone without it. Basically, it does what Dropbox does on your normal computer - and what the the name implies: it syncs folders between your different devices/computers/gadgets/servers.