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Box

Aaron Levie, CEO Capacity: 5 GB free; 25 GB for $9.99/month What it's for: Collaboration Killer feature: Users can brand Box-powered projects with their own logos and color schemes Funding: $287 million Number of users: 11 million Fun fact: Levie is an amateur magician

Dropbox

Drew Houston, CEO Capacity: 2 GB free; 100 GB for $10/month What it's for: Backups Killer feature: Syncs folders automatically on several devices Funding: $257 million Number of users: 50 million Fun fact: will.i.am is a fan

YouSendIt

Brad Garlinghouse, CEO Capacity: 2 GB free; 5 GB for $9.99/month What it's for: Sending files Killer feature: Send massive files with return receipts and download tracking Funding: $48.7 million Number of users: 34 million Fun fact: Used to produce Sesame Street

SugarSync

Laura Yecies, CEO Capacity: 5 GB free; 60 GB for $9.99/month What it's for: Backups Killer feature: Accessible on all operating systems and platforms Funding: $51.5 million Number of users: 25 million Fun fact: Popular with the Cannes set

Google Drive

Scott Johnston, product head Capacity: 5 GB free; 200 GB for $9.99/month What it's for: Documents Killer feature: Open and edit files from within a browser window Funding: Not applicable Number of users: 10 million Fun fact: Larry Page is a user, natch

Microsoft SkyDrive

Chris Jones, corporate VP, Windows Live Capacity: 7 GB free; 20 GB for $10/year What it's for: Documents Killer feature: Access files stored on a home PC from anywhere Funding: Not applicable Number of users: 60 million Fun fact: No fun fact available

6 cloud storage companies

Box

Dropbox

YouSendIt

SugarSync

Google Drive

Microsoft SkyDrive