Microsoft's (NASDAQ:MSFT) digital personal assistant, Cortana, is now publicly available for Google's Android operating system.

Although still in beta testing, Cortana for Android can be downloaded by anyone in the U.S. with a compatible handset. Given its increasing focus on search and the role it could play in preserving and strengthening the Windows ecosystem, Cortana for Android could eventually become one of Microsoft's most significant mobile apps.

G
Cortana running on Windows Phone. Photo: Microsoft

Cortana comes to...everything
Like Apple's Siri and Google Now, Cortana is a virtual assistant that responds to voice commands. In terms of its functionality, it's remarkably similar to these rival services, able to answer questions, conduct web searches, and set reminders (among other things). Like Google Now, it uses a system of interest cards based on relevant information (nearby venues, news, weather). Cortana started out as Windows Phone's answer to Siri, but Microsoft is in the process of porting it to a wide variety of platforms.

In addition to Android, Microsoft plans to bring Cortana to the iPhone, as well as its own Xbox One video game console. Most significantly, Cortana is a major part of Microsoft's Windows 10 operating system, built directly into the taskbar of any PC that runs Windows 10.

Unfortunately, its Android app is not nearly as capable as its Windows Phone alternative. Cortana for Windows Phone can open other apps, for example, and by uttering the phrase "hey, Cortana," can be accessed from anywhere in the Windows operating system. Cortana for Android lacks these features, and given that it's not directly integrated into the operating system, may never offer them. The same is likely to hold true when Cortana comes to the iPhone.

One Cortana across all your devices
Despite these limitations, its cross-platform compatibility could make Cortana for Android (and eventually iPhone) attractive to a wide variety of users.

Most Android handset and iPhone owners, assuming they own PCs, probably own PCs powered by Windows. Apple's Mac has made inroads in recent years, gaining share even as PC shipments decline, but Mac market share remains in the low double-digits overall. Google's Chromebooks, too, have seen their popularity surge, but sales remain modest relative to the broader PC market. Last year, Consumer Intelligence Research Partners released the results of a survey it conducted on recent iPhone buyers -- just 28% owned Macs.

When a user downloads Cortana for Android, they're prompted to sign into their Microsoft account. If they use the same account for their PC, Cortana will sync across their devices, sending them reminders on one device they've set on another, learning their preferences no matter which machine they happen to be using. Neither Siri nor Google Now offers anything like this. Even if an iPhone user happens to own a Mac, it doesn't support Siri. Google Now will send reminder cards to Chromebooks or the Chrome browser running on a PC, but can't be accessed directly from a PC.

More than 75 million PC owners have upgraded to Windows 10, and given that it's currently being offered as a free upgrade, more are likely to follow. If these users find Cortana to their liking, they could make an effort to install and use Cortana on their mobile devices.

Driving greater Bing engagement
For Microsoft, Cortana makes the Windows platform more compelling -- but more than that, it should benefit its search engine, Bing.

Bing lies at the heart of Cortana, powering the virtual assistant. More Cortana use could drive traffic away from Google, and result in Microsoft taking a larger share of the search market. Since its inception, Bing has been terribly unprofitable for Microsoft, literally costing the company billions. But Bing appears poised to finally achieve profitability. On the company's last earnings call, Microsoft CEO Satya Nadella said Bing would become profitable within the next fiscal year.

Cortana for Android could play a key role in driving Bing's profitability.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns and recommends AAPL, GOOG, and GOOGL. The Motley Fool owns shares of Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.