Microsoft today said it will make Windows free of charge for phones and tablets with screens smaller than 9 inches, a move designed to help boost the company's market share. The announcement comes alongside plans to let developers make universal applications that work on all devices running Microsoft's software — both Windows Phone and Windows. That feature is headed to Windows 8.1 as well as Windows Phone 8.1, which was also detailed on stage and is arriving on mobile devices in the next few months.

For smartphones and small tablets

Microsoft has been experimenting with a free, or low-cost version of "Windows 8.1 with Bing," which includes a handful of Microsoft apps and services aimed at Windows 7 users. It's unclear if this is the result of that effort. Microsoft simply referred to the new, free version as "Windows for Internet of Things," and is including a free year of Office 365.

Microsoft recently cut the price of Windows 8.1 licenses by 70 percent for some PC makers, reductions aimed at taking on low-cost tablets and Google Chromebooks that sell for less than $250. Previously Microsoft charged $50 per Windows 8.1 license.