MSDN subscribers can get Windows 8 from MSDN Subscriber Downloads. If you're not an MSDN subscriber, you can download an evaluation version of Windows 8 from Evaluation Center. (Note that this version will expire, and you cannot upgrade.)
Microsoft Visual Studio Express 2012 for Windows 8 is your tool to build Windows apps. It includes the Windows 8 SDK, Blend for Visual Studio, and project templates. You must first install Windows 8. Get details and additional languages.
Test your app before you submit it for certification and listing in the Windows Store. Learn more about the Windows App Certification Kit.
Download Visual Studio Extensions
Tools to help you localize your Windows Store app with translation support, translation file management, and editor tools. Get details and additional languages.
Standalone tools to easily install, test, and profile the performance of a Windows Store app on a PC running Windows 8 without Visual Studio 2012 installed. Get the Remote Tools.
A set of controls and APIs that enable apps to integrate Single Sign On (SSO) with your Microsoft account and access information from SkyDrive and Outlook.com. Learn more about the Live SDK.
Use advertising to monetize your applications while presenting a rich, engaging and immersive advertising experience to your users. Get the Windows 8 Ads SDK.
Add a scalable and secure cloud backend as well as incorporate structured storage, user authentication, and push notifications. Get Windows Azure Mobile Services.
Hundreds of samples from Microsoft can help jumpstart your project quickly. You can also download samples for a specific programming language, browse individual samples, copy code inline, and leave comments in the samples gallery.
Download Sample pack
Essential .psd assets including templates, common controls, and common components such as contracts, notifications, and tiles. Learn more about designing Windows apps.
Download design assets