Free Online File Backup Synchronization Services : A Quick Roundup

Dropbox

Dropbox is a storage application and service operated by Evenflow, Inc. The service enables users to store and sync files online and between computers. Dropbox has a cross-platform client (Windows, Mac and Linux) that enables users to drop any file into a Dropbox folder that is then synced to the web and the users' other computers with the Dropbox client. Files in the Dropbox folder may then be shared with other Dropbox users or accessed from the web. Users may also upload files manually through a web browser. A free Dropbox account offers 2 GB of storage. Users may upgrade to 50 GB or 100 GB by paying a monthly or yearly fee. The total amount of storage space of both the free and fee-based accounts may be increased by up to an extra 3 GB for free accounts and 6 GB for fee-based accounts by referring others to the service.

While Dropbox functions as a storage service, its focus is on synchronization and sharing. Dropbox synchronization uses SSL transfers with AES-256 encryption, and it supports revision history, so files deleted from the Dropbox folder may be recovered from any of the synced computers. Dropbox's version control also helps users know the history of a file they may be currently working on, enabling more than one person to edit and re-post files without complications of losing its previous form. There is no limit to file size for files added via the Dropbox application, but files transferred through the web interface are capped at 350 MB. Dropbox uses Amazon's S3 storage system to store the files.

The Dropbox service is similar to companies such as Box.net, Mozy, Wuala and Humyo. The company received seed funding from Y Combinator and Sequoia Capital.

Humyo

humyo.com is an online file storage service which synchronizes files across multiple computers and a remote data store. Files stored in humyo can be shared with other users and published on web pages. The company owns a former Bank of England bullion vault in which it houses the servers used to store its users data.
humyo.com was founded in 2007 by Dan Conlon (MD) and Peter Dubens (Chairman) and initially offered 30GB of storage space for free.
The company closed its beta in March 2008 with 100,000 users and by August 2008 had 215,000.
In October 2008, the company reduced the amount of storage space offered free of charge to new users to 10GB.

SpiderOak

SpiderOak is an online backup tool for Windows, Mac and Linux users to back up, share, sync, access and store their data using an off-site server. SpiderOak uses encrypted cloud storage and client-side encryption key creation, so even employees of SpiderOak cannot access users' information. SpiderOak distinguishes itself from competition in provision of encryption, in provision for syncing files and folders across multiple devices, and in automatic de-duplication of data.
SpiderOak offers two account types, a free 2 GB version and a SpiderOak Plus+ subscription. The paid plan starts at $10.00/month/100 GB increment.

Other Similar Free Services:
Syncplicity
Live Mesh