I'm thinking of something along the lines of Goodreads or LibraryThing... or even Steam. As these are both books and games (and some of them are free PDFs without even so much as an ISBN number), I'm wondering if anyone has discovered a good app/website for usefully tracking these things.
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The dedicated people over at RPGGeek maintain a database of RPGs, families of related RPGs, rule and source books, cover images, materials, accessories, ISBNs (where they exist), RPG designers, artists, and so forth. It's all categorised and items are linked together into their real-world relationships for easy searching and following of connections to related material and games.
It's almost exactly like LibraryThing/Goodreads but for RPGs. You can tracks the games you have (in multiple editions and versions) or have had in the past but traded away or sold. You can discover editions of games you didn't even know were published. You can also (if you like) track the sessions you have played each game, which are your favourites, and other such personal details. There is a trades feature so that you can compare your wishlist against others' lists of for-trade games and vice versa. The community is very active, and the site's integrated forums are some of the most civil I've ever participated in. Since the primary motive for joining the site is cataloguing and compiling a fair record of all RPGs and related items ever published, the community and its mods are mature and less concerned about arguing in an edition war than they are about sharing their love of the many RPGs out there.
In short, RPGGeek sounds like exactly what you're looking for, and I think you'll be very glad to explore it. As examples to start your exploration, here are the entries for Lady Blackbird and Mythender.
RPGGeek is run by the same software and people behind the immensely successful BoardGameGeek, so they have an excellent track record and are here to stay, so that putting work into cataloging your own collection or expanding the general database is a good investment of time.
You may want to check out reference management software, commonly used to organise scientific literature but it will probably suit your case.
From personal experience I can recommend Zotero. It is open source, you can attach pdfs (or any document) to placeholders, tag those placeholders and sort them in folders. Looking through libraries of a few hundred references - if properly organised - is pretty comfortable and fast.