I just kinda ...look at my bookshelf?I’m sure some of you have whole bookshelves of gaming materials that put my collection to shame, so… How do you manage it?
Another Librarything user - yet I still managed to buy a duplicate copy of d20 Past recently.
I've got about 3,700 RPG products listed there; no way I could remember all of those.
That makes perfect sense, except for when my collection gets close to complete, and I end up paying more than I want to for the last few items.I use a bookshelf. And I'm pretty familiar with what I have, as well as with what I don't have but want. I'm a collector, but not a completist, if that makes sense.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.