Productivity software-maker, Marketcircle, has been very busy this past year, releasing Mac and iPhone apps, and announcing an iPad app too. The company on Monday turned its attention back to the Mac with the release Billings Pro. Billings Pro is a multi-user time tracking and invoicing application targeted to small and medium size businesses. One of the big advantages of Billings Pro is that you’ll be able to use it anywhere — Mac, iPhone or on the Web.

“People came to us asking for a product like this and they have been asking for a while,” Alykhan Jetha (AJ), CEO of Marketcircle, told The Loop. “We realized that this made sense for the product, but what we didn’t want to do is just build a traditional clinet/server solution and we didn’t want to do something that was just web based.”

The solution Marketcircle came up with is largely based on the foundation of Billings 3, the company’s consumer-based product, and Billings Touch on the iPhone.

One of the added features in Billings Pro is Timecard. With its Web interface, Timecard allows users to track time, mileage, and expenses from any modern browser. According to Marketcircle you can use Internet Explorer, Firefox, Chrome, Safari, and mobile browsers for Android, Blackberry, iPhone, and iPad.

Jetha said the Web interface is all about entering information, so nothing slips through the cracks when billing time for a project.

Billings Pro also includes an approval process in its multi-user interface and over-the-air sync for the iPhone application.

Billings Pro includes over 30 professionally designed invoice templates, along with three specific templates for law and professional services.

For version 1, users can purchase Billings Pro for a one-time fee of $199.95 per user, with no monthly or yearly fees. Users can upgrade from Billings 3 to Billings Pro for $174.95 per user. For temporary users, Marketcircle offers a monthly per user “pay as you go” option for $24.95 as well.

Unlike many companies that chose to work either on the Mac or the iPhone, Marketcircle has been actively developing on both platforms, bringing its apps to even more people. While it’s been stressful at times, Jetha said it’s helped them move forward.

“It has been difficult, but we have the Daylite experience on our side,” said Jetha. “We have gone through the pains of client/server development and now we can draw on that.”

Jetha said that his engineers began working on mobile apps 10 minutes after the iPhone SDK was released and haven’t stopped since. Despite what many people think, it’s not always easy developing an iPhone app.

“It was harder for us to do a mobile app than a desktop because of the restrainsts of the screens and other factors,” said Jetha. “For instance, six engineers worked nonstop for a month to overcome a single problem.”

In the end it took Marketcircle one year, with four to eight engineers working on the project, to build the mobile app they wanted.