There are vast data archives exposed through private trackers that work on top of bittorrent. This isn't widely known due to their private, invite-only (and in some cases, entirely closed) nature but the fact remains that these exist and are fundamental in multiple, widely divergent communities.
Music, movies, tv, video games, books. Some trackers specialize in one type of content, some have everything.
Finding URLs of private trackers is trivial in google. Getting an invite usually requires knowing another user, unless they temporarily open signups for everyone.
