Helium.com
Helium.com, Inc. (formerly known as Helium Knowledge) is a website where writers can contribute articles for payment and visitors can read these articles for free. User generated content in a given category is rated up or down by other writers in a form of peer review system. As with social news sites like Digg or Reddit, user ratings determine the rank of an article. In this case, however, the users are the writers, and multiple answers/articles exist and compete in most topics. In turn, high-rated articles receive more page views and earn more money for writers. Critics have questioned the efficacy of this rating system and raised concerns about plagiarism, censorship, bans and other issues related to Helium.com.  According to Alexa's website global traffic rankings, Helium.com's rank has hovered around 10,000 since January 2007.  The site had over 5,000 users in October 2006.

# Articles
Contributors to Helium can write an article on any topic.  Articles are arranged by categories and sub-categories, e.g. Writing (main category) has sub-topics such as Creative Writing, Writing Tips, and The Business of Writing. Contributors may create their own topic, or post an article to an existing topic (which may have been created by another contributor, or by a Helium staff member), but each writer can only submit one article to any one topic.
If a contributor creates a new topic, it is not published immediately, but instead is held for vetting.  If approved, the topic is created and the article appears, usually within a day or two.  It is then open for other writers to contribute to.  Articles written to existing topics are published immediately and are not vetted or edited by Helium.
Articles within a topic compete with each other for "ratings".  Rating is done by contributors on a "rating screen" where the articles are shown anonymously, two at a time, and contributors are asked to vote for the better article. This process is repeated until all the articles in a given topic have been ranked in order.  Each time a new article is posted to a topic, the rating process is repeated.  Rating is anonymous to prevent bias by contributors.
There is a flagging system which enables contributors to report plagiarism and otherwise poor articles.

# Payment
All articles stay on the site in perpetuity and will continue to earn income so long as the writer is actively contributing to the site.  Writers earn a share of the ad revenue from ads appearing with their article, plus an amount based on the rating of their article and the number of times it is read.  Helium does not disclose how this formula is calculated.
Earnings vary considerably depending on the categories and topics chosen.  New writers can expect to earn only a few cents per article per month.  Successful writers typically have hundreds of articles on the site, and/or promote their work heavily elsewhere, and/or make major efforts in contests and the Marketplace (see below).
Writers are encouraged to promote their work by writing blogs which link to Helium, or on MySpace, Facebook, forums and social bookmarking sites - all of which can make a substantial difference to earnings. Writers can also win prizes varying from $25 to $300 in Helium contests, and submit work for purchase by publishers in the Marketplace section.  The winner of Helium contests is determined by ratings, however ratings have no bearing in the Marketplace section (although they are still conducted) - instead, the publisher is free to choose their preferred article for publication.
Helium earns money from Google AdSense advertisements displayed on the site, and from commission on articles sold to publishers on Marketplace.

# History
Previously HeliumKnowledge.com, Helium.com was launched in October of 2006. Initial press releases suggested the site was a quick-reference alternative to other sites like Wikipedia and Yahoo! Answers. The article review system for Helium was, from the start, touted by Helium as being significantly different than those of other encyclopedic sites. This review system has been the primary topic of numerous Helium press releases. More recently, Helium has increased rewards for affiliate marketers who bring new writers to the site. At present, according to Helium, the site has approximately 100,000 registered users, 30,000 of which are active contributors, and 300,000 total submitted articles.

# Criticism
Like any commercial website which is in the business of attracting contributors, Helium downplays criticism by contributors on its forums or in articles, and has been known to delete such references from the site. For the same reason, it actively promotes a positive image and contributions which "talk up" their site.
Most contributors agree that the rating system is imperfect, and there are often lively debates on this topic on the site.. Rating other articles benefits a given user, and there is no built-in penalty for giving a positive rating to an article with poor, plagiarized or incorrect content. Helium also does not allow users to flag articles for incorrect content, but only for offensive, plagiarized or poorly structured material.
Concerns have also been raised by writers who claim to have been banned from the site under false pretences. At least one writer has speculated openly that he was banned for raising issues of plagiarism and systematic rating manipulation on Helium. The Helium User Agreement enables Helium to keep all author content on Helium.com after banning an author. Banned authors are also denied the right to edit, remove or earn from content they submitted, including personal information created on their author biography pages.