Built because nothing quite like them existed. I have had these in mind for years, and even when you have the skills as a developer, you rarely have the time. With today's AI coding tools, building something like this finally takes an amount of effort I can justify.
Maybe others have the same problem: I love playing guitar but remember neither lyrics nor chords. SongBook Manager takes my favourite chord sheets from the usual sites and arranges them into books. The automatic layout is the part I use most, it prints pages that need as little page-turning as possible around a campfire.
There are plenty of tools for splitting and merging PDFs, but none of them is quick enough. This is my answer: drag the file into the window, split it, save it again.
I love painting in watercolour, but it always takes me a while to work up the nerve for a subject. Hours can go into finding the right reference photo. Wash Studio is where I prepare those references for painting.