Photobie is a free photo editor that includes an array of powerful and unusual features.
The program includes a decent selection of built-in filters, for instance, to sharpen, smooth, blur and otherwise apply special effects to your pictures. But it also supports Photoshop 8BF filter plugins, giving you easy access to thousands of additional creative possibilities.
If you're looking for fine control over your editing work then you'll appreciate Photobie's layer support, too - the program is packed with options to import, rearrange and manipulate layers to suit your needs.
Interesting 3D features include the ability to export your choice of layers to make a 3D cube. And the program can even import and display some 3Ds models, as well as the usual 2D image formats.
There's also an integrated screen grab tool, that can optionally import an image as a new layer. And Photobie can print images as PDF files, combine other images into animated GIFs, or build templates allowing you to save your pictures in attractive digital scrapbooks.