Reddit (stylized in its logo as reddit) is an American social news aggregation, web content rating, and discussion website. Registered members submit content to the site such as links, text posts, and images, which are then voted up or down by other members.
People come to Quora to ask questions about any subject, read high quality knowledge that's personalized and relevant to them, and share their own knowledge with others. Quora is a place to share knowledge and better understand the world.
Stack Exchange is a fast-growing network of 84 [and counting] question and answer sites on diverse topics from software programming to cooking to photography and gaming. We are an expert knowledge exchange: a place where physics researchers can ask each other about quantum...
4chan is a simple image-based bulletin board where anyone can post comments and share images. There are boards dedicated to a variety of topics, from Japanese animation and culture to videogames, music, and photography.Warning
4Chan is less moderated compared to other social networks and could be offensive to some people
News for nerds, stuff that matters. Slashdot (aka /.) is a technology-related news and discussion site with a focus on Linux, free and open source software and information freedom and privacy issues. The software it runs on, called Slashcode, is open source.