• Stack Exchange

  • "Super User" redirects here. For a user account with special privileges, see superuser .

    Stack Exchange is a network of question-and-answer (Q&A) websites on topics in diverse fields, each site covering a specific topic, where questions, answers, and users are subject to a reputation award process. The reputation system allows the sites to be self-moderating. [7] As of August 2019, the three most actively-viewed sites in the network are Stack Overflow, Super User, [8] and Ask Ubuntu . [9]

    All sites in the network are modeled after the initial site Stack Overflow, a Q&A site for computer programming questions created by Jeff Atwood and

    Joel Spolsky . Further Q&A sites in the network are established, defined and eventually – if found relevant – brought to creation by registered users through a special site named Area 51. [9][10]

    User contributions since May 2, 2018 are licensed under Creative Commons Attribution-ShareAlike 4.0 International , while older content is under Creative Commons Attribution-ShareAlike 3.0 Unported. [6][5]


    Foundation and growth

    In 2008, Jeff Atwood and Joel Spolsky created Stack Overflow, a question-and-answer web site for computer programming questions, which they described as an alternative to the programmer forum Experts-Exchange. [11] In 2009, they started additional sites based on the Stack Overflow model: Server Fault for questions related to system administration and Super User for questions from computer power users . [12]

    In September 2009, Spolsky's company,

    Fog Creek Software, released a beta version of the Stack Exchange 1.0 platform[3] as a way for third parties to create their own communities based on the software behind Stack Overflow, with monthly fees. [13] This white label service was not successful, with few customers and slowly growing communities. [14]

    In May 2010, Stack Overflow (as its own new company) raised US$6 million in venture capital from Union Square Ventures and other investors, and it switched its focus to developing new sites for answering questions on specific subjects, [14] Stack Exchange 2.0. Users vote on new site topics in a staging area called Area 51, where algorithms determine which suggested site topics have critical mass and should be created. [11] In November 2010, Stack Exchange site topics in

    "beta testing" included physics, mathematics, and writing.[15] Stack Exchange publicly launched in January 2011 with 33 Web sites; it had 27 employees [16] and 1.5 million users at the time, and it included advertising. [4] At that time, it was compared to Quora , founded in 2009, which similarly specializes in expert answers. [4] Other competing sites include WikiAnswers and Yahoo! Answers .[17]

    In February 2011, Stack Overflow released an associated job board called Careers 2.0, charging fees to recruiters for access, which later re-branded to Stack Overflow Careers. [18] In March 2011, Stack Overflow raised US$12 million in additional venture funding, and the company renamed itself to Stack Exchange, Inc. [19] It is based in Manhattan, New York City. [20] In February 2012, Atwood left the company. [21]

    On April 18, 2013 CipherCloud issued

    Digital Millennium Copyright Act (DMCA) takedown notices in an attempt to block discussion of possible weaknesses of their encryption algorithm. [22][23] The Stack Exchange Crypto group discussion on the algorithm was censored, but it was later restored without pictures.[24]

    As of September 2015, "Stack Exchange" no longer refers to the company, only the network of question-and-answer websites. Instead, the company is now referred to as Stack Overflow. [25]

    In 2016, Stack Exchange added a variety of new sites which pushed the boundaries of the typical question-and-answer site. [26] For example, Puzzling offers a platform for users who already know the answer to questions to challenge their peers to solve the problems unlike traditional Q–A sites where the poster does not know the answer. [26]

    Declining relationship between users and company

    In 2016, Stack Exchange announced the second iteration of the Stack Exchange Quality Project, in which they attempt to implement specific important features requested by the community to meet a distinct high-priority set of goals. After users enthusiastically responded with feature ideas, they complained that there was insufficient action on the company's part. [27]

    In October 2018, the company removed its Interpersonal Skills site from the Hot Network Questions list after a complaint on Twitter, and an employee (who was part of the SRE team, which was not community-facing) posted tweets attacking moderators. [28]

    On September 27, 2019, a moderator of multiple Stack Exchange sites was dismissed from her moderator position, allegedly connected to behavior associated with upcoming changes to the Code of Conduct (CoC) relating to

    gender pronouns .[29][30][31] Many other moderators resigned or suspended their moderator activity in response to the dismissal. The company responded with two very-poorly-received messages which have since been deleted, [32] and by a slightly less negatively-received apology several days later.[33] In December 2019, the company posted a message, stating that they and the moderator had come to an agreement and expressing regret for any damage to her reputation. [34][35] Nevertheless, this, plus the sudden departure of multiple community managers (Stack Exchange employees who interact with the community), led to an erosion of trust between the community and the company — convincing many of the site's most prolific users, including many community-elected moderators and a community manager, to depart within the next few months. [36][37][38]

    2019–2020 licensing change announcements

    On September 2, 2019, the terms of service (and the footer of every page served) changed to referencing the "Creative Commons Attribution-ShareAlike" (CC BY-SA) license's 4.0 version instead of its 3.0 version. [39] Users were puzzled as to how Stack Overflow acquired the rights for this relicensing of their past contributions, [40] with some users explicitly stating that they did not intend their contributions to be licensed under CC BY-SA 4.0. [41][42] Users were concerned that, if the relicensing was found to be a breach of CC BY-SA 3.0, Stack Exchange would have made itself unable to distribute the content under any CC BY-SA license (and that the footer's license statement could be erroneous), and would have to rely on its "perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works and store" the content instead. [43] On September 27, an official Stack Exchange reply stated it had been an "important step", but declined to discuss with the community the legal basis for the relicensing. [44]

    In March, 2020, a post announced that content contributed before May 2, 2018 was available under a CC BY-SA 3.0 licence. [6] In the ensuing discussion, several users asked about the similar situation in August 2010, when Stack Exchange switched from accepting CC BY-SA 2.5 contributions to 3.0. A representative of the corporation noted "we are looking [...] to show v2.5 for posts predating this change but cannot commit to it yet". Some users were unconvinced that the September 2019 announcement wasn't a breach of CC BY-SA 3.0 that would have caused its termination, and some answers weren't placated by the dateline chosen. [45]

    Site features

    The primary purpose of each Stack Exchange site is to enable users to post questions and answer them. [15] Users can vote on both answers and questions, and through this process users earn reputation points, a form of

    gamification .[21][46] This voting system was compared to Digg when the Stack Exchange platform was first released. [13] Users receive privileges by collecting reputation points, ranging from the ability to vote and comment on questions and answers to the ability to moderate many aspects of the site. [46] Due to the prominence of Stack Exchange profiles in web search results and the Stack Overflow Careers job board, users may have reason to

    game the system . [18] Along with posting questions and answers, users can add comments to them and edit text written by others. [47] Each Stack Exchange site has a "meta" section where users can settle disputes, in the style of MetaFilter 's "MetaTalk" forum, because the self-moderation system for questions and answers can lead to significant arguments. [48]

    Notable parts of Stack Exchange include sites focused on physics, [49]

    video games, [50] and patents.[51]

    All user-generated content (questions and answers) posted on the Stack Exchange Network is copyright by the contributor and licensed to Stack Exchange under a Creative Commons Attribution Share Alike (CC-BY-SA) license. [21][52]

    Technologies used

    Stack Exchange uses IIS , SQL Server , [53] and the ASP.NET framework, [53] all from a single code base for every Stack Exchange site (except Area 51, which runs off a fork of the Stack Overflow code base[54] ). Blogs formerly used WordPress , but they have been discontinued.[55] The team also uses Redis , HAProxy and

    Elasticsearch. [53]

    Stack Exchange tries to stay up to date with the newest technologies from

    Microsoft, usually using the latest releases of any given framework. The code is primarily written in C# ASP.NET MVC using the Razor View Engine. The preferred IDE is Visual Studio and the data layers uses Dapper for data access. [56]

    Site creation process

    Every new site created in the Stack Exchange Network goes through a detailed review process consisting of six steps: [10][57][58]

    1. Discussion: The Stack Exchange meta site should provide a forum for discussing potential new ideas labeled a future Stack Exchange site.

    2. Proposal: A public proposal must be drafted and posted so that any member of the community can discuss the proposal and vote on it. This allows a collaborative proposal to emerge over time. The proposal must address these four key issues:

    1. the topic of the site

    2. the targeted audience

    3. forty exemplary questions, upvoted at least 10 times from the community

    4. sixty followers from the community

    3. Commitment: 200 users interested in the new site are asked to formally commit and support the site by actively participating and contributing to it.

    4. Private Beta: If the concept receives 100% commitment, the site enters the private beta phase, where committed members begin actively using the site and publicizing it.

    5. Public Beta: The site is open to the public for a long period. This allows the creators to ensure that the site reaches critical mass before it is fully launched.

    6. Graduation: The site is evaluated on multiple criteria such as the number of answered questions, new questions per day, and registered users. If it meets these criteria and is deemed "sustainable", it is granted a "graduation" and fully launched.

    Notable alumni and users

    Nobel Prize winners

    Gerard 't Hooft [59]

    Fields Medal winners

    Peter Scholze [60] (2018)

    Martin Hairer[61] (2014)

    Terence Tao [62] (2006)

    Tim Gowers[63] (1998)

    Curtis McMullen [64] (1998)

    Richard Borcherds [65] (1998)

    Edward Witten [66] (1990)

    Vaughan Jones[67] (1990)

    Michael Freedman[68] (1986)

    William Thurston [69] (1982)


    Joel Spolsky (co-founder of Stack Overflow)[70]

    Jeff Atwood (co-founder of Stack Overflow)[71]

    Aaron Swartz (co-founder of


    Ravi Vakil (co-founder of

    MathOverflow )[73]

    Notable scientists and mathematicians

    Ian Agol[74]

    John Baez [75]

    Carlo Beenakker[76]

    Andreas Blass [77]

    Robert Bryant [78]

    Nike Dattani [79]

    Noam Elkies [80]

    Matthew Emerton[81]

    Alexandre Eremenko [82]

    Joel David Hamkins (top user on

    MathOverflow )[83]

    James E. Humphreys [84]

    Gil Kalai [85]

    Anna Krylov [86]

    Greg Kuperberg [87]

    Joseph O'Rourke [88]

    Igor Rivin [89]

    Jeffrey Shallit (Computer Scientist with Erdos number of one)[90]

    Peter Shor (from Shor's Algorithm)[91]

    Michael Shulman [92]

    Neil Strickland [93]

    Xiao-Gang Wen

    Gjergji Zaimi [94]

    See also



    Q&A software


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    27. ^ "Answer by user jscs to We need to stop hoping for change in, or help from, SO Inc" . Retrieved

    March 5, 2020.

    28. ^ "Revisiting the "Hot Network Questions" feature, what are our shared goals for having it?" . Retrieved March 5, 2020.

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    32. ^ "An Update to our Community and an Apology" . Archived from

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    33. ^ An apology to our community, and next steps

    34. ^ Update: an agreement with Monica Cellio . Meta Stack Exchange . Retrieved 2020-01-03.

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    41. ^ Owens, Thomas. " 'I do not grant anyone the right to change the license of my contributions' " .

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    45. ^ " "Under CC BY-SA 3.0, any violations terminate (sic) your CC license" " . Retrieved March 8, 2020.

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    58. ^ "Changes to Stack Exchange – Stack Overflow Blog" . Retrieved

    January 19, 2016.

    59. ^ "Gerard 't Hooft" .

    60. ^ "Peter Scholze" .

    61. ^ "Martin Hairer" .

    62. ^ "Terence Tao" .

    63. ^ "Tim Gowers" .

    64. ^ "Curtis McMullen" .

    65. ^ "Richard Borcherds" .

    66. ^ "Edward Witten" .

    67. ^ "Vaughan Jones" .

    68. ^ "Michael Freedman" .

    69. ^ "Bill Thurston" .

    70. ^ "Joel Spolsky" .

    71. ^ "Jeff Attwood" .

    72. ^ "Aaron Schwartz" .

    73. ^ "Ravi Vakil" .

    74. ^ "Ian Agol" .

    75. ^ "John Baez" .

    76. ^ "Carlo Beenakker" .

    77. ^ "Andreas Blass" .

    78. ^ "Robert Bryant" .

    79. ^ "Nike Dattani" .

    80. ^ "Noam Elkies" .

    81. ^ "Matthew Emerton" .

    82. ^ "Alexandre Eremenko" .

    83. ^ "Joesl David Hamkins" .

    84. ^ "James E. Humphreys" .

    85. ^ "Gil Kalai" .

    86. ^ "Anna Krylov" .

    87. ^ "Greg Kuperberg" .

    88. ^ "Joseph O'Rourke" .

    89. ^ "Igor Rivin" .

    90. ^ "Jeffrey Shallit" .

    91. ^ https://stackexchange.com/users/508412/peter-shor?tab=accounts

    92. ^ "Michael Shulman" .

    93. ^ "Neil Strickland" .

    94. ^ "Gjergji Zaimi" .

    External links

    Official website

    List of Stack Exchange sites

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