Since my computer OS is Linux, most programs are free. Here are the main ones I currently use:
GIMP. (Image editing, and general retouching).
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Free Optional Plugins. (To expand the capabilities of GIMP).
RAWTherapee. (For RAW image processing, also works with JPG/TIFF, very powerful program).
DigiKam. (For photo management (i.e. tags, ratings, albums, advanced search tool, etc.).
Hugin. (For panorama stitching).
I find the programs to be very powerful, useful, versatile -- and the best part is -- free!
Hugin, I still have a little trouble understanding, but the others are quite easy to use.