As promised at WinHEC, Microsoft has made available the first generally available pre-releases of the Windows 10 WDK and Hardware Lab Kit (WLK).
The kits are available here: http://dev.windows.com/en-US/featured/hardware/windows-10-hardware-preview-tools
Also available (from the same page) are VS 2015 CTP 6 and the pre-release of the Win10 SDK (both of which you’ll need for the Win 10 WDK).
Several Windows Universal Driver samples are also available for download.