For some time I've been wanting to start recording all the books I check out from the library for M and C. I could have just made a list of them in a Word document but I wanted a way to tag and organize them by categories with some books in multiple categories. What I need is something similar to the way iTunes organizes music with a general library and then the ability to group those songs into different playlists except my playlists would be book categories. I haven't figured out a way to do exactly what I want (working within the constraints of my system and budget) but I have developed a workable substitute in Omni Outliner.
I made an outline of all my books separating them into categories by type: baby board books, short picture books, long picture books, easy readers, chapter books. For each entry, you can make notes so in the notes section I add tags like: Halloween, animals, anatomy, fall, etc. I can then do a search of the document to find all books with the word "animals" in the notes.