More than 53 million individuals in the US—roughly a third of the workplace—make money doing something that isn't a traditional 9 to 5 job, according to recent numbers from the Bureau of Labor Statistics. That number has grown tremendously over the last few years, thanks at least in part to new ways of bringing in income (at least part-time). Platforms like Uber, Etsy, eBay, and Airbnb are taking the boss out of the traditional work relationship. Most freelancers and independent contractors who aren't a regular part of a company's payroll report directly to a new manager: the customer.

Those millions of self-employed people need ways to manage their money. Some may have businesses that are complex enough to require the use of small business accounting software, such as QuickBooks Online or Xero. But many freelancers have needs that are simpler, and that require remote access at least part of the time.

There are numerous iPhone apps that will accommodate their needs without piling on a lot of unnecessary features (and cost). I've reviewed five of them here: GoDaddy Bookkeeping Essentials, Harvest Solo, Intuit QuickBooks Self-Employed, IQBoxy Prime, and Xero TaxTouch.

These apps handle one or more of a number of essential tasks for freelancers and independent contractors who want to:

Connect to Online Bank and Credit Card Accounts

Getting daily, real-time updates of account transactions and balances is critical, especially if you're operating on a thin margin. GoDaddy Bookkeeping Essentials, QuickBooks Self-Employed, and Xero TaxTouch make this possible. All you have to do is enter the login credentials that you use to access your online bank and credit card accounts.

The apps download all cleared transactions—usually once daily—and deposit them in a register where you can add more detail like categories. If you mix business and personal transactions in your accounts, you can separate them.

Record and Store Receipts

If you've ever filed income taxes as a self-employed individual, you know how important it is to have receipts backing up your business expenses. The IRS accepts credit card and bank account statements as proof, but they must contain the amount paid and a description of the purchase indicating that it was for a business expense. All of the apps reviewed here track expenses and receipts.

You can manually enter any expense transaction by filling in blank fields and/or selecting options from existing lists you've created (payee, category, etc.). Every app I looked at with the exception of Xero TaxTouch lets your iPhone work as a camera, so you can snap photos of receipts and attach them to your own record. IQBoxy Prime takes this a step further. It uses Optical Character Recognition (OCR) to read details on your receipts and fill in details on your records automatically—and quickly. This advanced use of technology helped earn IQBoxy Prime a 4-star rating, though it lacked many features offered by competitors.

Track Time and Mileage

If you get paid by the time increment worked, you can track your hours using GoDaddy Bookkeeping Essentials or Harvest Solo; the latter even includes a built-in timer. And except for IQBoxy Prime, all the apps that I reviewed offer a separate record form for entering the mileage you've driven for business. QuickBooks Self-Employed will measure your trip mileage automatically using the iPhone's Location Services.

Accept Web-Based Payments

Paper checks are so twentieth century. If you're not allowing your customers to pay with a credit or debit card, you're losing business. GoDaddy Bookkeeping Essentials and Harvest Solo let you set up a merchant account with services such as PayPal or Stripe, so you can receive payments electronically.

Categorize Transactions

Nothing says 1995 like poring over your bank account and credit card statements to find tax-deductible deductions does. If you wait until the end of the year—or even the quarter—to do this, you've probably forgotten much about what each transaction represents, and whether you can claim it on your Schedule C.

GoDaddy Bookkeeping Essentials, QuickBooks Self-Employed, and Xero TaxTouch let you categorize business transactions by standard IRS Schedule C categories for tax purposes. They learn from your classification and automate the process in later transactions. You can also set up your own rules, so that transactions are assigned the same category every time. You can, of course, override those settings for individual purposes.

Calculate Estimated Taxes

As a self-employed individual, you know that the IRS requires you to estimate and pay the taxes that would be due on your income every quarter, instead of waiting until you prepare your annual return. There are penalties for not doing so. To make that task simpler, faster, and more accurate, GoDaddy Bookkeeping Essentials, QuickBooks Self-Employed, and Xero TaxTouch do the calculating for you based on the income and expenses you've entered and your tax profile information.

Integrate App Data

Two of these apps, GoDaddy Bookkeeping Essentials and Harvest Solo, require some activity on their corresponding websites. You'll do some of your setup there, for example. You can also create invoices on the Harvest Solo site that can be viewed, sent, and paid on the app. GoDaddy Bookkeeping Essentials' website fleshes out the tools and data found on the app; it's also where you must visit to learn what your estimated tax payments should be. You can generate invoices on the app itself.

GoDaddy Bookkeeping Essentials has another attribute that is unique in this group: You can import sales data from sites, such as Etsy and PayPal.

If your business is complex enough that you're using an online accounting application like QuickBooks Online or Xero, you can share your app's data with them. Harvest Solo has the most generous integration options; it can be used with more than 70 add-ons. IQBoxy Prime can be integrated with multiple accounting and cloud storage/backup services.

Finally, QuickBooks Self-Employed Tax Bundle ($17.99 per month) is an enhanced version of QuickBooks Self-Employed. Using it, you can export your tax-related data to TurboTax. The monthly charge includes one free filing using Intuit's tax application.

A Worthy Group

GoDaddy Bookkeeping Essentials wins our Editor's Choice because it offers the most functionality and flexibility at the lowest price. Its user experience is not my favorite in this group, but the user interface and navigation system make it possible to use just a subset of its features without the rest getting in the way. It could, in fact, offer fewer tools and still justify its subscription price.

Harvest Solo is the only app that really challenges GoDaddy Bookkeeping Essentials in terms of its capabilities; it could also be implemented in a team setting. The app would have recieved a higher ranking, but for one restriction: You must tie each expense to a project or client. Not everyone structures their businesses in that way.

But all of the apps I tested here do what they do quite well. Most in this eclectic group take advantage of the iPhone's capabilities, and each one is easy to set up and use. Depending on your needs, each could be a valuable addition to your mobile office.