#7 Square

Estimated Value: $3.2 billion

Last Year's Rank: #14

Business: Accept credit card payments anywhere with your iPhone, iPad or Android phone

Location: San Francisco, California

CEO: Jack Dorsey

It is an electronic payment service, provided by Square Inc. Square allows users in the United States to accept credit cards through their mobile phones, either by swiping the card on the Square device or by manually entering the details on the phone. While there are a lot of mobile payment solutions, Square is really attacking the cash register space and it's on-boarding small businesses quickly.

Now, Square is processing U.S. credit and debit transactions for Starbucks which is huge: Starbucks' annual sales in fiscal 2011 were almost $12 billion, about two-thirds of that in the United States.

#6 Dropbox

Estimated Value: $3.5 billion

Last Year's Rank: #6

Business: Dropbox is a free service that lets you bring your photos, docs, and videos anywhere and share them easily.

Location: San Francisco, California

CEO: Drew Houston

It is a file hosting service operated by Dropbox, Inc. that offers cloud storage, file synchronization, and client software. In brief, Dropbox allows users to create a special folder on each of their computers, which Dropbox then synchronises so that it appears to be the same folder (with the same contents) regardless of the computer it is viewed on.

Dropbox has about 50 million users and it generated an estimated $240 million last year. The company’s worth is estimated to be $3.5 billion.