WindowWatchScreenshot 

 

WindowWatch is a tool that developers and Webmasters can use to quickly preview the results of their efforts. It locks onto whatever window is currently active on your desktop and lets you manipulate it in a variety of ways, displaying it in various screen resolutions. You can instantly resize a window to any standard desktop size and modify the tool`s built-in desktop settings or add several of your own, without altering your computer`s settings

Screenshot of WindowWatch