Time Keeper! works on a hierarchy of three elements: Clients, Projects (which are assigned to clients), and Times / Costs (assigned to projects). Once the application is launched, you can begin by adding a client at a particular rate. Time Keeper! allows any currency to be entered for the rate, making it easy to charge clients in their local currency.
Once you've entered some of the necessary information about the main timekeeping elements, it's time to get to work! When you arrive at a client's office or being work on a project, you can launch the app, enter a title for the work you are performing, and then tap the Start button to begin an hour:minute timer. You don't need to stay in the app to continue tracking time; if your work requires you to use other iPhone apps, Time Keeper! continues to log the time in the background.
Likewise, you can stop the clock for such important tasks as lunch, playing DoodleJump for two hours, or seeing what's new on your Facebook account. Once you've actually completed your task, you "commit" the task by tapping on the appropriate button at the bottom of the Time Keeper! screen.
The best feature of Time Keeper!, in my opinion, is the ability to blast out nice looking HTML invoices directly from the app. I don't know how many times I've been working with a client, told them I'd send them an invoice, and then promptly forgot about it for a couple of weeks. With Time Keeper's invoicing capability, I could generate and send an invoice on the spot, hopefully resulting in more timely payment.
The invoices aren't too customizable, but they provide just enough information to make them usable. Users can create a starting invoice number, add their company name, and even provide a text footer by entering the appropriate information into Settings. I found that if I saved a company logo in Pastebot, I could simply copy it and paste it to the top of the invoice before sending. If you're confused about the workings of Time Keeper! when you start using it, there is a very useful built-in help file that is also accessible from the Settings screen. I highly recommend looking at the help file before starting to use the app -- Time Keeper! can be a bit confusing at first if you just try jumping immediately into using it.
In terms of the competition, there's no lack of similar apps in the App Store. For example, there's Timewerks: Mobile Billing [$9.99, iTunes Link], which integrates with the Credit Card Terminal app from Inner Fence [US$0.99, iTunes Link] to allow you to invoice clients and receive payment all from the cozy confines of your iPhone screen. For good-looking invoices, Invoice2Go [US$9.99, iTunes Link] provides templates that are attractive and customizable.
Those who are using Freshbooks for their accounting will enjoy MiniBooks for Freshbooks [US$14.99, iTunes Link], which not only provides on-the-spot invoicing from an iPhone, but also gives you access to all of your accounting information from anywhere with a data connection.
Last, but certainly not least, users of Marketcircle Billings for Mac will be pleased to know that the company is beta-testing Billings Touch, an iPhone companion to the desktop application. Although I haven't seen or used the app as of this writing, if it is as user-friendly and well-designed as Marketcircle's Daylite Touch app, it will be a winner.
For now, however, I've found that Time Keeper! is all I need, and at US$2.99 it's a bargain compared to most of the other invoicing and timekeeping apps. Be sure to check out the gallery for some screenshots of Time Keeper! in action, and let us know about your favorite timekeeping app in the comments.