Developers working on Windows 10 apps can now download a new preview version of its SDK tools. They are designed to be used on preview builds of the OS that have version numbers of 14267 and above.
"The Preview SDK is a pre-release and cannot be used in a production environment. Please only install the SDK on your test machine. The Preview SDK Build 14267 contains bug fixes and under development changes to the API surface area. If you are working on an application that you need to submit to the store, you should not install the preview. This is a pre-release of the Windows 10 SDK. This release should only be installed on test machines, and is not supported in a production environment. The APIs and software included in this preview should not be expected to be final and may not be included in the commercial version."
A list of what's been fixed, along with known issues with this SDK preview build, is available on Microsoft's site.