Microsoft might very well be gearing up to launch a Google Chromecast rival. While the tech giant hasn't announced anything official yet, one of its latest FCC filings details a device codenamed HD-10, which features WiFi, HDMI support and a USB connection. Those three will sound familiar if you know what the Chromecast is, but what really demystifies the device's nature is a separate document on the WiFi Alliance website. That filing, unearthed by Nokia Power User, called the HD-10 a "Miracast Dongle." Miracast, as you might know, is Microsoft's screen-sharing technology available on Windows 8.1, Windows RT and, most recently, Windows Phone 8.1, though it's also built into Android 4.2 (and later) and BlackBerry 10.2.1.