I use the free version of Adobe Photoshop (CS2 9.0.0) (http://www.snapfiles.com/get/photoshopcs2.html), you can edit gifs but I never learned how.
An alternative to PS is PhotoFiltre (http://www.snapfiles.com/get/photofiltre.html), has a lot of features.
A must have in my opinion is PicPick 4.1.5 (http://www.snapfiles.com/get/picpick.html), which takes screen shots, edits and a lot more.
All of these are freeware BTW. 😉
Plus it’s just a very convinient Tool all around to have. I use it every Day. Primarily for
Signature-making back in the Day, nowadays mostly to edit Covers.
Except, if you care about it being legal, freeware-wise………………..
Learn to use avisynth/vapoursynth and use ImageMagick and FFMPEG to process everything. Just for cutting and resizing. Some advanced recoloring, but not nearly as advanced as doing stuff like rainbows and other things that Adobe PS can do.
Of course, you can be the Gold Pirate and just pirate any version of Adobe PS.