SageThumbs is a powerful shell extension allowing to preview enormous amount of image formats directly in Windows Explorer by using Pierre-e Gougelet's GFL library (XnView's author).
As SageThumbs is a Windows Explorer context menu extension, there is no an executable file that you should launch to bring it up. To use it, just open any folder with image files in Windows Explorer, and then right-click a file you want to preview. You'll see the thumbnail immediately in the context menu.
SageThumbs can use external XnView plugins (more plugins). If XnView is installed to the registry, SageThumbs will find the proper plugin folder paths.
If XnView is not installed, the plugins should be unpacked and placed in the default install location of XnView dependent on the bit depth:
${Env:ProgramFiles(x86)}\XnView\PlugIns\$Env:ProgramFiles\XnView\PlugIns\