reddit

reddit is a social news
website where users can post links to content on the web. Other users
may then vote the posted links up or down, causing them to appear more
or less prominently on the reddit home page.

The site has discussion areas where users may discuss the posted
links, and vote for or against others' comments. When there are enough
votes against a given comment, it will not be displayed by default,
although a reader can display it through a link or preference. Users
who submit articles which other users like and subsequently "vote up"
receive "karma", points which a user receives as a reward for
submitting interesting articles.

reddit also includes several topical sections called subreddits, which focus on specific topics, including programming and science.

Taking an idea from Google, the reddit logo changes for various holidays and often for no reason at all, paying homage to Star Wars, classic video games, and geek culture in general. There is an archive of the logos at redditalien.com.

Source - Wikipedia

Digg

Digg is a community-based popularity website with an emphasis on technology and science articles, recently expanding to a broader range of categories such as politics and entertainment. It combines social bookmarking, blogging, and syndication with a form of non-hierarchical, democratic editorial control.

News stories and websites are submitted by users, and then promoted
to the front page through a user-based ranking system. This differs
from the hierarchical editorial system that many other news sites
employ.

Source - Wikipedia

del.icio.us

A non-hierarchical keyword categorization system is used on del.icio.us where users can tag each of their bookmarks with a number of freely chosen keywords (cf. folksonomy). A combined view of everyone's bookmarks with a given tag is available; for instance, the URL "http://del.icio.us/tag/wiki" displays all of the most recent links tagged "wiki" (more about navigating tags). Its collective nature makes it possible to view bookmarks added by similar-minded users.

del.icio.us has a "hotlist" on its home page and "popular" and "recent" pages, which help to surface interesting content and make the website an effective conveyor of popular internet memes and trends.

Many novel features have contributed to making del.icio.us the most popular service of its kind. These include the website's simple interface, human-readable URL scheme, a novel domain name, a simple REST API, and RSS feeds for web syndication.

Use of del.icio.us is free. The source code of the site is not available, but a user's own data is freely downloadable through the API in an XML or JSON format, and can also be exported to a standard Netscape bookmarks format.

Everything posted to del.icio.us is publicly viewable by default, although a user can mark specific bookmarks as private, and imported bookmarks are private by default. The public aspect is emphasized; it is not focused on storing private ("not shared") bookmark collections. Many people use the del.icio.us linkrolls, tagrolls and network badges to display their links and information on their weblogs. Others use the RSS feeds and "daily blog posting" feature to do this.

There are a few open source clones of del.icio.us, such as de.lirio.us and sa.bros.us, as well as competing social bookmarking services, such as Simpy, Furl, BlinkList, and Netvouz.

del.icio.us was acquired by Yahoo! on December 9, 2005. Various guesses suggest it was sold for somewhere between US$15 million and US$30 million.

The del.icio.us domain name is a notable example of a domain hack, an unconventional combination of letters to form a word or phrase. del.icio.us, though not the first domain of this nature, is the best-known and most frequently-accessed domain hack, and the Yahoo! acquisition is the highest-profile acquisition of a domain in this category. However, delicious.com and delicio.us also redirect to the del.icio.us website.

Source - Wikipedia