DirectX SDK Debug Layer: For Windows 10 Technical Preview (9926 or later), you need to enable the debug layer as a Windows optional feature to successfully use
D3D11_CREATE_DEBUG_DEVICE or the Visual Studio 2013 Graphics Diagnostics tools: Start -> Settings -> System -> Optional features -> Add a feature; select "Graphics Tools". See this post for details.
Win32 desktop games: The existing guidance for quality Win32 desktop games running on Windows 7, Windows 8.0, and Windows 8.1 all applies to Windows 10 as well (see Desktop Games on Windows 8.x). Note that there is a new
<compatibility> manifest section GUID for Windows 10 (see Manifest Madness), and
VerifyVersionInfo is now subject to the same manifest-based behavior as
Enterprise: If you are curious about the business version of Windows 10, see this post.
Web developers: The Technical Preview includes IE11, but there are a few improvements for Windows 10.
Windows Store and Windows phone developers: See this post.
Command Prompt: There's some fun features added for Windows 10's command prompt. See this post.