The Free and Open Source Software for today is Nomacs | Image Lounge!
Nomacs is an image viewer with some basic editing capabilities. The best thing about Nomacs is its support for a wide range of file formats and conversion capabilities. I use the program extensively and it is smooth.
If you need a good program for viewing or editing multiple formats of images, Nomacs is great. It's available for Windows, Mac, Linux, BSD and others. Check it out!