Microsoft's plan to make its new version of Windows a mobile hit by letting it accept tweaked Apple and Android apps has met an obstacle: some software developers the company needs to woo just aren't interested.
Windows phones accounted for just 3 percent of global smartphone sales last year, compared with about 81 percent for devices with Google's Android system and 15 percent for Apple and its iOS system, according to research firm IDC. One reason is that Windows doesn't run as many or as attractive apps as its rivals.
To boost sales of its phones and new operating system, Microsoft said last month that it would provide tools to software developers to make it easier to design apps for Windows based on apps that run on Android or Apple.
But because so few people use a Windows phone, most developers remain focused on the more popular systems and don't see a need to develop apps for Windows. They also said they doubt how easy the new tools will be to use.
"Windows phone will have to gain a significant share of the market before this becomes something that saves us time and/or money," said Sean Orelli, a director at app development firm Fuzz Productions in New York, which makes apps related to Citibank, the New York Post, and Conde Nast, among others.
For Microsoft, the world's biggest software company, there's a lot at stake as it rolls out Windows 10.
If developers don't embrace the new platform, it will seriously damage the prospects of the new operating system, which Microsoft hopes will power one billion devices in two or three years.
Interviews with more than a dozen developers found just one planning to move an app from Apple or Android to Microsoft.
That's King.com, which ported its popular Candy Crush Saga game from iOS to Windows 10 "with very few code modifications" and will be installed automatically with upgrades to Windows 10, according to Microsoft. King.com confirmed the move but declined to comment further.
Eight developers said they aren't planning to develop for Windows 10 at all. Four who already have Windows apps said they would continue to do so.
Because Microsoft hasn't actually unveiled its new set of tools to turn apps into a Windows format, developers did not rule out any move, and a Microsoft spokesman said that "it is still early" and many software companies want to explore the tools over the coming months.
More and better apps might attract more people to buy a Windows phone or tablet, Microsoft reasons.
Only six of the top 10 free apps on iPhone are available for Windows phone, and of those, two are made by Microsoft itself. In the past Microsoft has paid developers to create Windows apps.
Failure to attract the apps would not be fatal for Microsoft, which is growing more reliant on its Office, server software and cloud computing services, but it would be a sign that Microsoft is losing its hold on personal computing, in a world where phones are expected to outsell PCs by more than six to one by 2017.
Because of that trend, "it's going to be hard for developers to prioritise building for Microsoft," said John Milinovich, chief executive of URX, a mobile ad service that creates links between apps.
Windows, closely tied to the stagnant PC market, is a big but static business for Microsoft.
It's likely worth US$20 billion in revenue this fiscal year, analysts say, compared with almost US$30 billion for its Office business, out of total expected annual revenue of US$93 billion.
The company's server software and cloud computing businesses are growing much faster, with cloud computing revenue forecast to triple to US$20 billion by 2018.
Even though only a handful of developers have been allowed a sneak preview of the new tools Microsoft says it's preparing, most doubt it will be easy to take iOS and Android apps to Windows.
Concerns include how the Windows app will use batches of libraries an app needs to run, and the prospects that Apple's new language, Swift, may soon eclipse the current one.
Erik Rucker, head of mobile at Smartsheet, which makes an online tool to manage projects, said he doesn't plan a Windows app version. He doubts tweaking an iPad or iPhone app for Windows would be simple.
"We'd end up writing a whole bunch more code," to move over an Apple app that was tightly integrated with the device, he said.
For Jason Thane, general manager at General UI, a mobile app developer, the cost of developing a Windows app from another system would need to fall to about 10 percent to 20 percent of the cost of building it.
"It can cost 50 percent or more of the cost to develop an app on one platform to port it to a new platform," said Thane, who hasn't yet used the new tools.
"So if Microsoft has a way for our customers to do it easily and cheaply, and if there's no serious performance or functionality impact, I think they'd have a lot of people wanting to do it."
Even a little extra effort is too much for some smaller developers, including former Microsoft executive Adam Tratt, who now runs Haiku Deck, which makes presentation software primarily designed for iPads.
"I'd like to at some point, but we're not working on it yet," he said. "It's a function of resources."
Recent history hasn't been on Microsoft's side. Last year Pinterest pulled its Windows Phone test app, and this year Chase and Bank of America stopped supporting Windows phone apps, saying few customers were affected. None of those companies would comment on plans for Windows 10.
Microsoft does have some loyal supporters. Walt Disney, Netflix and USA Today all confirmed they are developing apps for Windows 10.
USA Today is building a "universal" app for Windows, which will run across PCs, tablets and phones. But instead of reusing code from its existing Windows apps, or porting from Apple or Android, the development team opted to start fresh.
The best experience was always going to be achieved with tools made for a given software system, said Christopher Kamsler, manager of mobile development, and even with those his team had to tweak the app to work for different sized devices.
It's an uphill battle for Microsoft, according to Frank Gillett, an analyst at tech research firm Forrester.
"Android and iOS are in the zone, the Windows guys just aren't there yet," he said.