How it works: The Windows version of the ZumoDrive desktop application that I tested works similarly to the OpenDrive system: It creates a virtual drive on your desktop that's linked to your online storage space on ZumoDrive's servers. To sync files and folders, you drag and drop them into this virtual drive, and they will be automatically uploaded to your account.
You can share a folder or file with others by right-clicking on the folder or file and, within the pop-up menus, entering the e-mail address of the person to whom you're granting access. You can also make ZumoDrive generate a hyperlink to one of your folders or files for posting on the Web.
What's good: Compared to Dropbox's and OpenDrive's desktop clients, ZumoDrive has more functionality -- though mainly for tweaking mundane technical details like how it interacts with your network. But it includes convenient features for sharing media files among your computers and mobile devices. For example, it has a function that helps you easily provide remote access to your iTunes music and playlist.
Like Dropbox, the ZumoDrive client software is available for several operating systems and mobile platforms.
What needs to be fixed: Since the free versions of Dropbox and ZumoDrive have similar features, ZumoDrive's biggest "fault" may be that it isn't as popular as Dropbox, so chances are that the people you want to collaborate with may be using Dropbox instead of ZumoDrive.
Bottom line: ZumoDrive is the best alternative and strongest challenger to Dropbox in this roundup. It matches Dropbox in terms of basic features, but it allows you to do more directly from its desktop client.
OS: Windows XP/Vista/7, OS X 10.5 and later, Ubuntu Linux 8 and higher, Fedora Linux 9 and higher, various other Linux distros
Mobile apps: Android, iPhone, WebOS
Storage size:1GB storage; up to an additional 1GB upon doing specific sign-up tasks (syncing your files to your ZumoDrive user account, installing the desktop client software, etc.)
Maximum file size: None
Daily data-transfer limit: None
Paid plans: Plans range from $2.99/month for 10GB to $79.99/month for 500GB
Dropbox, OpenDrive and ZumoDrive represent best the concept of cloud-based file storage, syncing and sharing: Their desktop programs embed a virtual drive within the file structure of your operating system. Their premise is to work as invisibly as possible by functioning like a normal drive.
OpenDrive gives you the most online space for free -- but I occasionally encountered problems when trying to sync/upload files that were a couple of megabytes in size through its Java-based desktop client.
Between Dropbox and ZumoDrive, it's pretty much a draw. If you have colleagues or friends who already use Dropbox, that could give it the edge. Still, you may want to check out ZumoDrive and open a free account, since its desktop client includes built-in features that make it convenient and easy to share your media among your various devices.
Howard Wen reports on technology news, trends and products as a frequent contributor to Computerworld and Network World.
This story, "Free online services that store, sync and share your files" was originally published by Computerworld.