There are about 100,000 applications in the Windows Store, an online marketplace that launched in October. That trails the more than 800,000 apps each available for Android and iOS, Dan Farber notes. "The only thing we know for sure is that the APIs, tools and approaches of different platforms will continue to evolve and diverge. Working across platforms will only get more difficult, not easier," Steven Sinofsky, formerly of Microsoft, wrote in a blog post. Separately, Microsoft said it will release Windows 8.1 to PC manufacturers next month.