Photo Editing Programs What Are Some Great Free Photo-editing Programs?

What are some great free photo-editing programs? - photo editing programs

I know some great Photoshop and image editing programs. My friends showed me a great line, as Picnik, but it says something about downloading a demo version of some program called Corelia or something of that nature.
Can someone please check whether (Corelia) an image editing program, and who know others?