Windows 7: These updates to the rating systems apply to Windows 7 as well when KB2773072 has been installed. PEGI (Finland) and OFLC (Australia) are present after the update, but are marked deprecated in the UI as end-users are encouraged to switch to the newer systems.
Windows 8.1: This release includes two changes to the rating systems:
Windows 8: KB 2838466 updates Windows 8 with support for PCBP (Russian Age Rating System)
Windows Store apps: See MSDN for details on Age ratings and rating boards, as well as this post
Windows phone apps: See MSDN for details about Game ratings
The DirectX SDK has historically been the shipping vehicle for the various Game Explorer tools. With the transition to the Windows SDK (see Where is the DirectX SDK?), these tools now have new homes:
Game Definition File Editor (GDFMaker.EXE) is in the Windows 8.x SDK (included with Visual Studio 2012 and available standalone). It is located in the x86 directory under the bin folder. This version of the tool uses the ratings systems descriptions available on the version of Windows it is run on, rather than including a local copy as the older DirectX SDK version did. This means you should run it on Windows 8 be able to populate all the latest ratings information, although the tool can be run on Windows 7 as well only showing the rating systems available for Windows 7. The Windows SDK version requires .NET 4.x as well. This tool is used to author GDF files for both Win32 desktop and Windows Store apps.
Windows 8.1 SDK: There's an updated version of GDFMaker.EXE (included with VS 2013 and available standalone) that resolves a problem when run on English but not EN-US systems.
Game Definition File Validator (GDFTrace.EXE) is available on MSDN Code Gallery and has been updated for these latest rating systems changes and can build without requiring the DirectX SDK using Visual Studio 2010 or Visual Studio 2012.
Gameux Install Helper (GameuxInstallHelper.DLL) is available on MSDN Code Gallery. It has been updated from the DirectX SDK (June 2010) version and can build without requiring the DirectX SDK using Visual Studio 2010 or Visual Studio 2012. This utility is used for deploying Win32 desktop applications.
Update: These tools are also included in the DirectX SDK samples repo on GitHub.
For publishers and developers of games on Windows 7, be sure to read Desktop Games for Windows 8 Consumer Preview for recommendations on compatibility for existing Win32 desktop style applications as well as the official Compatibility Cookbook.