Internet properties established in 2003

4chan is an anonymous English-language imageboard website. Launched by Christopher "moot" Poole in October 2003, the site hosts boards dedicated to a wide variety of topics, from video games and television to literature, cooking, weapons, music, history, technology, anime, physical fitness, politics, and sports, among others. Registration is not available, except for staff, and users typically post anonymously. As of 2022, 4chan receives more than 22 million unique monthly visitors, of whom approximately half are from the United States.

Clips4Sale (C4S) is an adult video content selling website and is known for fetish content. It launched in 2003. Clips4Sale is the largest clip site on the internet with over 8 million clips and 105,000 independent content producers on its platform. It is based in the United States, with an overseas branch registered in Cyprus for EU/EEA operations.

Rooster Teeth Productions, LLC was an American entertainment company headquartered in Austin, Texas. Founded in 2003 by Burnie Burns, Matt Hullum, Geoff Ramsey, Jason Saldaña, Gus Sorola, and Joel Heyman, Rooster Teeth was a subsidiary of Warner Bros. Discovery Global Streaming & Interactive Entertainment, which is a division of Warner Bros. Discovery.

PLOS (for Public Library of Science; PLoS until 2012 ) is a nonprofit publisher of open-access journals in science, technology, and medicine and other scientific literature, under an open-content license. It was founded in 2000 and launched its first journal, PLOS Biology, in October 2003.

Hostinger is a web hosting company. Established in 2004, the company is headquartered in Lithuania and employs about 900 employees.

Kinopoisk (Russian: Кинопоиск, a portmanteau of "cinema" and "search") is a Russian online database of information related to films, TV shows including cast, production team, biographies, plot summaries, ratings, and reviews. Since 2018 (as КиноПоиск HD) also a subscription video on demand streaming service with several thousand films, TV series, cartoons and including premieres and exclusive ones, has also been available.

Torrentz was a Finland-based metasearch engine for BitTorrent, run by an individual known as Flippy and founded on 24 July 2003. It indexed torrents from various major torrent websites and offered compilations of various trackers per torrent that were not necessarily present in the default .torrent file, so that when a tracker was down, other trackers could do the work. It was the second most popular torrent website in 2012.

Harry Potter Fan Zone is an Australian Harry Potter fansite created in 2003 by Australian teenager Andy McCray. Harry Potter author J. K. Rowling awarded the website a "Fan Site Award", stating that "[it] is a great Australian site with an impressively young staff who have produced some really insightful editorials."

Adam4Adam is an online dating website designed for men to meet other men "for friendship, romance, or a hot hookup".

Typepad is a blogging service owned by Endurance International Group, previously owned by SAY Media (from the merger of Six Apart and VideoEgg).