Cloud storage services like Dropbox are incredibly convenient, but that convenience comes with a price: your data is stored in a place where others can get at it, and the only things preventing that from happening are the service's own security and privacy policies and practices. It's also costly to keep large amounts of data in sync—most services will give you a few gigabytes for free, and then charge monthly or yearly fees for larger quantities.

Some services, like SpiderOak, attempt to address the security problem by removing themselves entirely from the encryption process and ensuring that they never have access to the keys to your data, but storing more than documents still requires an investment in relatively expensive server-side storage (and as we noted in our review, the service's interface leaves a bit to be desired). Some other vendors offer "personal cloud" services which allow you to access your local files from elsewhere, but these can lack the OS integration and ease-of-use which the ubiquitous Dropbox presents.

If you're looking for something that will let you use your own server for storage and looks and acts pretty much like Dropbox, AeroFS might be for you. The service is still in an invite-only beta as of this writing, but with just a few additions it could be the locally hosted Dropbox that some Windows, OS X, and Linux users have waited for.

Basic operation

After getting your invite and downloading the software, you'll be prompted to create an account. This sign-in exists only so that your Aero FS-running computers can get the 2048-bit RSA encryption keys keys they need—your computers then authenticate against each other using these keys, and can do so even if the AeroFS servers are down. Your data is fully encrypted before being transferred to other computers, preventing it from being intercepted and decoded in transit.

Installing the AeroFS software creates a folder in your user profile, much like Dropbox does, and this can be changed from the default location as desired. In both Windows and OS X, AeroFS automatically adds a link to your shared folder in the Favorites section of the Windows Explorer and Finder, respectively. Once you've installed AeroFS on more than one system, everything placed in this folder is automatically propagated to all of your other AeroFS-linked computers.

Aside from the security advantages of keeping all of your file syncing and data transfers local (once you've installed the AeroFS software and authenticated, an Internet connection is no longer required), AeroFS frees you from the limited amount of storage space provided by other cloud service vendors. The size of your "personal cloud" is limited only by the amount of disk space on your various computers.

Sharing files between AeroFS users is slightly more complicated than with Dropbox, but it's still not difficult. First, click the AeroFS tray icon, click Share Folder, and select the folder you'd like to share.

You'll then be presented with a dialog box with a customizable message asking for an e-mail address to share with. That person will then be sent an eight-character code; on the receiving end, you click the AeroFS tray icon again, click "Accept Invitation," and input the code to gain access to the shared folder.

Shortcomings

The sync and sharing features work and work well, but that's the easy part—Dropbox also has fairly robust versioning, deals with conflicting files reasonably seamlessly, and lets you access your files from just about anywhere, including your Web browser, smartphone, or tablet of choice.

The versioning system in AeroFS is also perfectly usable—click "Version History" in the tray icon menu and you can go through all of your files and folders to see their previous versions. AeroFS will keep storing older versions as long as there is sufficient free local disk space; if your disk gets too full, it will begin silently deleting the very oldest items to make more room.

One thing that doesn't work quite as well is the way AeroFS handles file conflicts. To test this, I created a text file, typed some information into it, and saved it to my AeroFS folder. To make sure syncing was working, I opened up the document on one computer at a time and typed in additional text—sure enough, the changes would propagate to each system pretty much instantly as I made edits.

Then, I paused syncing on both systems, made more changes to the text file on each system, and then re-enabled syncing. Each system would continue displaying notifications as I made changes, giving me the impression that my changes were being sent out, but in reality each computer was treating its version as the definitive version. I could find the other computer's copy of the file in the Version History window, but otherwise there was no indication that anything was wrong.

I didn't lose any data because of this—both versions of the documents were still present on both computers. But where Dropbox automatically creates a separate version of the file and renames it to indicate which of your systems it came from, AeroFS simply behaves as if everything is working as it should. This could be a problem if all of your systems aren't always on at the same time—it's not something that's likely to happen if you have an always-on "server" running AeroFS, but conflict management is a major concern in any file syncing solution, and AeroFS's could be better.

And finally, we get to AeroFS's biggest shortcoming, which is lack of access from Web browsers or mobile devices. Dropbox (and, for that matter, Google Drive, SugarSync, Box.com, and most of the other major players in this field) offers apps for iOS and Android as well as a robust Web client that can be used to access your files while on public computers. There are probably ways around this problem—an intrepid DIYer could probably set up a WebDAV server pointed at their AeroFS folder to enable Web and mobile access—but it's too bad that such a major piece of functionality is missing from the main package.

Conclusions

AeroFS is still in beta, and the problems we had with it may well be ironed out by the time it's actually ready for public release. As it stands, the product works best if you're a security-minded individual or small business with a server dedicated to synchronizing files among many clients. The software can also be used at home to synchronize files between, say, a desktop and laptop that aren't always on at the same time, but the conflict management problems we had might cause problems if you're not careful.

When things are working, though, AeroFS provides an experience that's nearly as seamless and simple to explain as Dropbox, but with the added security that comes from keeping your data (and data transfers) confined to your devices rather than on someone else's server. The level of OS integration present and its ease of configuration make it one of the most promising "personal cloud" solutions we've seen so far.