If you've ever used Windows Explorer, surely Free RAW Viewer will not be a challenge for you. As its name indicates, this is a tool for displaying images in RAW format.
Free RAW Viewer is a simple and austere program, with an interface divided into two parts: the left is the tree of the system, and right thumbnails RAW images that are in the folder. When you click on the image, it is shown on full screen.
Besides that, this utility supports the display of images of various other formats other than RAW (supports BMP, GIF and JPEG).
You already know: if you need a swift program to display images, Free RAW Viewer is one of the best options on which you can rely.