If there were prizes for flexibility in formats, then ToyViewer would surely be up there, supporting absolutely everything from TIFF to obscure formats like XBM and MAG.
Just a handful of the formats ToyViewer can support are TIFF, GIF, BMP, PNG, JPG, BIE (JBIG), PCX, PCD, PICT, PNM (PPM, PBM, and PGM), XBM, MAG, SUN Rasterfile, JPEG2000 ( JP2, JPC, J2K), and many more. You can convert and save in a rather more limited number of formats, although this includes TIFF, PDF, GIF, BMP, PNG, JPG, JPEG2000, BIE (JBIG), PNM and XBM.
ToyViewer lets you perform a variety of basic editing and manipulation procedures, including resizing and rotating images. The contrast and color can be adjusted and you can enhance the appearance of the images as well as editing the metadata tags. Beyond this the editing options in ToyViewer are limited. You can create animated GIFs and TIFF Stacks although loading animated GIFs is hit and miss - some animated GIFs are simple not supported. Despite it's flexibility, there are some other formats that don't display well too including TIFFS compressed by JPEG, some SVG images and JPEG2000 images.
The overall interface is simple, if a little uninspiring. It seems many of the translations have been made badly from Japanese to English, meaning it can be a bit confusing in places.
ToyViewer isn't the most glamorous image editor and manager out there but in terms of format support, it's second to none.