I recently made a Calibre library for mine, but I don't have a ton of stuff yet. Calibre is designed for organizing ebooks. It's only downside is that it's got a specific way it organizes folders and files, so I've got all the files duplicated so I can find them easily by system. In Calibre I've got them tagged with the system, if it's a supplement, how many players, what equipment is needed, etc