Cloud computing is an information technology (IT) paradigm that enables ubiquitous access to shared pools of configurable system resources and higher-level services that can be rapidly provisioned with minimal management effort, often over the Internet. Cloud computing relies on sharing of resources to achieve coherence and economies of scale, similar to a public utility.
Third-party clouds enable organizations to focus on their core businesses instead of expending resources on computer infrastructure and maintenance. Advocates note that cloud computing allows companies to avoid or minimize up-front IT infrastructure costs. Proponents also claim that cloud computing allows enterprises to get their applications up and running faster, with improved manageability and less maintenance, and that it enables IT teams to more rapidly adjust resources to meet fluctuating and unpredictable demand. Cloud providers typically use a "pay-as-you-go" model, which can lead to unexpected operating expenses if administrators are not familiarized with cloud-pricing models.

Here are the some apps that is using for Cloud Computing.

Microsoft Office 365
Office 365 is the brand name Microsoft uses for a group of subscriptions that provide productivity software and related services. For consumers, the subscription allows the use of Microsoft Office apps on Windows, macOS, iOS, Android and Windows 10 Mobile, provides storage space on the OneDrive file hosting service, and grants 60 Skype minutes per month.

Saleforce
Salesforce is an American cloud computing company headquartered in San Francisco, California. Though its revenue comes from a customer relationship management (CRM) product, Salesforce also sells commercial applications of social networking through acquisition and internal development.

BOX
Box based in Redwood City, California, is a cloud content management and file sharing service for businesses. The company uses a freemium business model to provide cloud storage and file hosting for personal accounts and businesses.[6] Official clients and apps are available for Windows, macOS, and several mobile platforms. Box was founded in 2005.
Full list here: http://www.businessinsider.com/the-most-popular-cloud-apps-used-at-work-2015-8#no-7-zendesk-a-customer-support-technical-support-service-1118