If you are a developer and have been waiting patiently for the Windows 10 SDK, Microsoft has released the bits and you can download it at the source link below. For those not familiar, an SDK is a software development kit that assists in the creation of software and in this case, apps for Windows 10.
If you are looking for more tools to help build a Windows 10 app, Microsoft has launched a page that has all of the required items along with other helpful resources for developers here.
Download: Windows 10 SDK