It is the Gimp of book management.
Both Calibre and Gimp are great examples of outsider design.
Works amazingly well.
Looks amazingly bad.
What does that even mean. It is design produced by the user and maker of the app. If you hire a designer that's neither, doesn't that actually make them the outsider?
He's not making a traditional art form as someone who's untrained. He's designing Calibre, and he's the most qualified person in the world in doing that.
Frankly? Who care. Napster had even worst GUI, yet it has become popular as it just did the job people wanted.
So true. Main thing is both are still being built and used everyday though.