Krita is a free and open source application that can be used to create book covers. It is not unlike GIMP, and it has a few advantages. First, it supports CMYK color profiles, which is preferred for printing book covers. It also supports drawing tablets for artistry and fine-tuning elements of a book cover which cannot be accomplished as easily in GIMP. The major disadvantage to Krita is the text editing is still very clunky and hard to use.

Taken together, Krita is a great application and should be used where needed for some stylistic book cover design work. It also supports the same non-destructive layer styles that Photoshop supports making it a great FOSS application for transitioning out of subscription software.