photoQT
PhotoQt is a popular, fast and simple photo viewing application which has a graphical interface which is highly configurable. This app lets the user utilize several keys or mouse shortcut keys for multiple features and also enables help for any kind of external script command to be run easily. If the user of this app wishes to browse and sort images from different folders then the file management option can used. The program is written in QT/QML. PhotoQt is a versatile application. The application supports a variety of file types and is used to view PSD, XCF, PDF, and PS files. The Windows version has one limitation: it doesn't support RAW images, although the developer has indicated that support is on the way. 
Why you must get it: 
PhotoQt app has many features which include displaying thumbnails of the original picture before showing off the enlarged version, slideshow options, zooming, rotating, flipping, and display of the massive amount of data or metadata in which one file will be connected to another. Users can also make the desired image the wallpaper directly from the viewing window, handle file management, scaling, use face tags using XMP metadata, integration and merging of multiple images from the libraries and so on. You can change the desktop wallpaper to a photo or view slides of photos in a folder. Using the "filter images in a folder" option, you can find images by name or extension. The program can display photo metadata and histograms. The Settings page has a plethora of options that are fairly simple to use, and if you're not sure what something does, hover your mouse over it to see a tool-tip that clarifies what the configuration is for. You can log in to your Imgur account from the Settings menu to directly upload files to the cloud.