With more than 500,000 apps available for smartphones and tablets, there’s nothing you can’t do on the fly—from tracking surf conditions to starting your car. Some are now standard-issue biz tools, such as Google docs, Outlook and Microsoft Office. But for many people, there are specific killer apps they can’t work without. Here are five.

FOR CONSULTANTS AND MOBILE WORKERS

Killer App: Dropbox

What it is: A secure file-hosting service

What it does: Dropbox lets you store documents, photos and videos on a server that you can access from any synched phone or computer, as well as from the Dropbox website. When you’re done viewing or working on them, it saves them in all places. You can also set up sharing privileges.

Why it kills: “All of my sensitive documents are stored on the secure server, in addition to the hard drive on my PC,” says Andrew Schrage, owner and operator of the blog, Money Crashers Personal Finance based in Chicago. “The basic membership is free, and it comes with 2GB of storage space, which is more than enough for what I currently need.”

FOR SALES MANAGERS

Killer App: Salesforce and Salesforce Chatter

What it is: Salesforce CRM is a Customer Relationship Manager; Salesforce Chatter is an employee social network.

What it does: Salesforce uses cloud computing to let companies and individual salespeople integrate all aspects of their business—from account history to customer communication to workflow. With Chatter, employees can collaborate in real time via instant message.

Why it kills: “I can select one of my salespeople’s customers, see the correspondence and the details of the opportunity, and access the contract,” says John Golden, CEO and President of Huthwaite, a global sales-training and consulting firm based in Arlington, VA. “It’s a composite picture of what’s happening with the customer—and I can get it quickly and easily. It’s a one-stop place to manage your business.”