This is a remarkably popular and prolific freeware image viewer and converter. The list of file types supported is one of its greatest attributes. See for yourself:
In addition to extensive file type support, this utility also offers:
Multi-language support
Thumbnail and preview options
Slideshow
Drag and drop
Fast directory viewing
Batch conversion
E-mail options
Audio CD player
Print options
Color depth adjustment
Scan support
Cut and crop
Effects (sharpen, blur, Photoshop filter factory)
Image capturing
Extracts icons from EXEs and DLLs
Lossless JPG rotation
Many hotkeys
Many command-line options
Another feather in the Irfanview hat is their bragging right to serving as the first Windows graphic viewer in the world to offer animated-GIF support. With options like these, why would you need anything else?