The Decompiler window invoked from Visual Studio can also be used separately. The standalone Decompiler executable is located in the extension folder. You can access it using the CodeRush | Support | Extension Folder... Visual Studio menu item.
In the extension folder, run the Decompiler\DecompilerApp.exe application. The standalone decompiler is similar to the Visual Studio decompiler window, except for the inability to load solution and project references.