Facebook

Facebook is an online social networking service headquartered in Menlo Park, California. Its website was launched on February 4, 2004, by Mark Zuckerberg with his Harvard College roommates and fellow students Eduardo Saverin, Andrew McCollum, Dustin Moskovitz and Chris Hughes. The founders had initially limited the website's membership to Harvard students, but later expanded it to colleges in the Boston area, the Ivy League, and Stanford University. It gradually added support for students at various other universities and later to high-school students. Since 2006, anyone who is at least 13 years old was allowed to become a registered user of the website, though the age requirement may be higher depending on applicable local laws.Its name comes from a colloquialism for the directory given to it by American universities' students.After registering to use the site, users can create a user profile, add other users as "friends", exchange messages, post status updates and photos, share videos and receive notifications when others update their profiles.Additionally, users may join common-interest user groups, organized by workplace, school or college, or other characteristics, and categorize their friends into lists such as "People From Work" or "Close Friends". Facebook had over 1.18 billion monthly active users as of August 2015.Because of the large volume of data users submit to the service, Facebook has come under scrutiny for their privacy policies. Facebook, Inc. held its initial public offering in February 2012 and began selling stock to the public three months later, reaching an original peak market capitalization of $104 billion. On July 13, 2015, Facebook became the fastest company in the Standard & Poor’s 500 Index to reach a market cap of $250 billion.

Twitter

Twitter is an online social networking service that enables users to send and read short 140-character messages called "tweets".Registered users can read and post tweets, but unregistered users can only read them. Users access Twitter through the website interface, SMS, or mobile device app. Twitter Inc. is based in San Francisco and has more than 25 offices around the world.Twitter was created in March 2006 by Jack Dorsey, Evan Williams, Biz Stone and Noah Glass and launched by July 2006. The service rapidly gained worldwide popularity, with more than 100 million users who in 2012 posted 340 million tweets per day.The service also handled 1.6 billion search queries per day.In 2013 Twitter was one of the ten most-visited websites, and has been described as "the SMS of the Internet.As of May 2015, Twitter has more than 500 million users, out of which more than 302 million are active users.Twitter's origins lie in a "daylong brainstorming session" held by board members of the podcasting company Odeo. Jack Dorsey, then an undergraduate student at New York University, introduced the idea of an individual using an SMS service to communicate with a small group.The original project code name for the service was twttr, an idea that Williams later ascribed to Noah Glass,inspired by Flickr and the five-character length of American SMS short codes. The decision was also partly due to the fact that domain twitter.com was already in use, and it was six months after the launch of twttr that the crew purchased the domain and changed the name of the service to Twitter.The developers initially considered "10958" as a short code, but later changed it to "40404" for "ease of use and memorability."Work on the project started on March 21, 2006, when Dorsey published the first Twitter message at 9:50 PM Pacific Standard Time (PST): "just setting up my twttr".Dorsey has explained the origin of the "Twitter" title:

...we came across the word 'twitter', and it was just perfect. The definition was 'a short burst of inconsequential information,' and 'chirps from birds'. And that's exactly what the product was.

Google+

Google+ is an interest-based social network that is owned and operated by Google Inc.The service, Google's fourth foray into social networking, experienced strong growth in its initial years, although usage statistics have varied, depending on how the service is defined. User engagement has been relatively low.Three Google executives have overseen the product, which is undergoing substantial changes. These include the re-launch of two core Google+ functions, communications and photos, as standalone products, as well as refocusing the service on shared interests. Males of ages 24–36 have comprised the largest share of the user base.Google+ is the company's fourth foray into social networking, following Google Buzz (launched 2010, retired in 2011), Google Friend Connect (launched 2008, retired by March 1, 2012), and Orkut (launched in 2004, as of 2013[update] operated entirely by subsidiary Google Brazil – retired in September 2014).Google+ launched in June 2011. Features included the ability to post photos and status updates to the stream or interest based communities, group different types of relationships (rather than simply "friends") into Circles, a multi-person instant messaging, text and video chat called Hangouts, events, location tagging, and the ability to edit and upload photos to private cloud-based albums

Opera

Opera is a web browser developed by Opera Software. The latest version is available for Microsoft Windows, OS X, and Linux operating systems, and uses the Blink layout engine. An earlier version using the Presto layout engine is still available, and additionally runs on FreeBSD systems.Opera siblings – Opera Mobile, Opera Mini and Opera Coast – work on devices running Android, iOS, Windows Phone, Symbian, Maemo, Bada, BlackBerry and Windows Mobile operating systems, while Opera Mini runs on Java ME-capable devices.According to Opera Software, the browser had more than 350 million users worldwide in the 4th quarter 2014.Total Opera mobile users reached 291 million in June 2015.Opera has been noted for originating many features later adopted by other web browsers. A prominent example is Speed Dial.Opera began in 1994 as a research project at Telenor, the largest Norwegian telecommunications company. In 1995, it branched out into a separate company named Opera Software ASA.Opera was first released publicly with version 2.0 in 1996,which only ran on Microsoft Windows.In an attempt to capitalize on the emerging market for Internet-connected handheld devices, a project to port Opera to mobile device platforms was started in 1998.Opera 4.0, released in 2000,included a new cross-platform core that facilitated creation of editions of Opera for multiple operating systems and platforms.

Skype

Skype is a telecommunications application software product that specializes in providing video chat and voice calls from computers, tablets, and mobile devices via the Internet to other devices or telephones/smartphones.Users can also send instant messages, exchange files and images, send video messages, and create conference calls. Skype is available to download onto computers running Microsoft Windows, Mac, or Linux, as well as Android, Blackberry, iOS, and Windows Phone smartphones and tablets. Much of the service is free, but users require Skype Credit or a subscription to call landline or mobile numbers. Skype is based on a freemium model. As of February 2012, there were 34 million concurrently online on Skype;at the end of 2010, there were over 660 million worldwide users with an average of over 100 million active each month.First released in August 2003, Skype was created by Dane Janus Friis and Swede Niklas Zennström in cooperation with Estonians Ahti Heinla, Priit Kasesalu, and Jaan Tallinn, who developed the backend, which was also used in music-sharing application Kazaa.In September 2005, eBay acquired Skype for $2.6 billion.In September 2009, Silver Lake, Andreessen Horowitz, and the Canada Pension Plan Investment Board announced the acquisition of 65% of Skype for $1.9 billion from eBay, valuing the business at $2.75 billion. Skype was later acquired by Microsoft in May 2011 for $8.5 billion. Microsoft's Skype division headquarters are in Luxembourg, but most of the development team and 44% of the overall employees of the division are still situated in Tallinn and Tartu, Estonia.Skype allows users to communicate by voice using a microphone, video by using a webcam, and instant messaging over the Internet. Skype-to-Skype calls to other users are free of charge, while calls to landline telephones and mobile phones (over traditional telephone networks) are charged via a debit-based user account system called Skype Credit.