Strictly speaken for me I don't need some fancy GUI.
I keep all my ebooks on my desktop (I currently read on laptop) in an directory tree structure.
I have divided my maps according to subject (math, IT, physics, ...) and depending on the map (eg IT) I make subdirectories depending on the specific subject (eg Oracle).
This allows me to find any book rather quick (search function windows
)
If I were to have a non-pc based device than I would not add more than 10 books and keep the desktop (or external HD) as a central repository.