See also BitTorrentTrackers.

BTDig.com (née BTDigg) is a DHT search engine, indexing mainline DHT torrents and the files they contain.

TorrentHistory also tracks torrents on the mainline DHT, indexing the torrents, info hashes, and the associated files. The site does not post full info hashes.

BitTorrent v2

Reddit: Is anyone else excited about per-file hashes in Bittorrent v2?

BiglyBT Swarm Discoveries

BitTorrent v2 libtorrent support announcement

Bencode

bencode online displays torrents (bencoded files) as a JSON representation, lets you modify, and export as a torrent file again.