Photomania is a full featured, free photo editing, viewing and cataloging app.
Although not the smartest looking photo editor on the block, Photomania has a lot going for it. It has a large, clear editing interface that can be modified to your tastes. The basic toolbar is easy to use and perfect for photo viewing, while the very bottom of your screen gives you a handy summary of your photo's properties. Photomania also has good configuration options, and supports an impressive range of files -
Photomania can be used as a photo cataloger, as well as a viewer, allowing you to create HTML albums and slideshows and save to PDF. There are more tools apart from the editing ones - you can do batch conversions, set images as wallpaper, add frames and more.
Interestingly for a free application, Photomania has some interesting and extensive photo editing options. Those not so comfortable with the technical options can use the Wizard under Tools, while those who want the hands-on approach should take a look at Photomania's Effects options. Here you'll be able to rotate and resize images, and also to tweak technical specifications and add effects.
Photomania looks dated, but it's free and perfect for tweaking your photos' technical specs.