Usenet: Usenet is a search service, not entirely unlike Google or Bing, that allows users to focus their searches on specific fields of information, types of information, or specific types of data, such as photographs or videos. The first Usenet search is said to have been carried out in the 1970s, effectively predating any modern internet search engines by decades.
Originally, Usenet was only used between closed loops of computers, making it more like a search engine for local area networks on a macro scale. Today, the majority of web users have no idea what Usenet is used for, or that it even exists. However, as the popular tech site Gizmodo writes, the search platform is extremely popular among those who spend a lot of time and bandwidth downloading multimedia -- legally or otherwise.
In this way, Usenet's ability to search out specific types of data has made it an extremely popular medium for finding everything from movies to music to eBooks. Because the service ultimately fell to the wayside as the internet and services like Google saturated the tech space, Usenet is largely unregulated, meaning those looking for freebies have found Usenet to be a safer and faster way to go.
This isn't to say all Usenet activity is piracy-related. Usenet clients are also quite popular among academics. The service's ability to search for specific information makes it a far more efficient alternative to finding scholarly articles, for example, than the shotgun search methods made popular by the big internet search providers.