Mosaic is the browser which popularized the World Wide Web. It was also a browser for earlier concepts such as , Usenet, and [(protocol)|Gopher]. Its clean, easily understood, user interface; reliability; availability for the Windows platform; and ease of installation all contributed to make it the application which opened up the Web to the general public. In addition, Mosaic was the first browser to implement images embedded in the text, rather than displayed in a separate window.
Mosaic was developed at the National Center for Supercomputing Applications (NCSA) beginning in late 1992. NCSA released the browser in 1993, and officially discontinued development and support on January 7, 1997. However, it can still be downloaded from NCSA
Mosaic was the final link in the chain of technologies (TCP, IP,  | nntp | [(protocol)|gopher] | , URL, HTML, etc.) which Tim Berners-Lee had earlier brought together to invent the World Wide Web. After the appearance of Mosaic the concept of the World Wide Web took off globally at an explosive rate.
Mosaic was born very mature. Fifteen years later the most popular browsers, Internet Explorer and Mozilla Firefox, retain many of the characteristics of the original Mosaic graphical user interface (GUI) and interaction experience.
Before these, 0.1~0.9 was developed.
Development of Mosaic began in December 1992. Version 1.0 was released on April 22, 1993, followed by two maintenance releases during summer 1993. A port of Mosaic to the Commodore Amiga was available by October 1993. Version 2.0 of NCSA Mosaic was released in December 1993, along with version 1.0 releases for both the Apple Macintosh and Microsoft Windows. An Acorn Archimedes port was underway in May 1994.
The licensing terms for NCSA Mosaic were generous for a proprietary software program. For all versions non-commercial use was generally free (with certain limitations). In addition the X Window System/Unix version publicly provided source code (source code for the other versions was available after agreements were signed). Despite persistent rumors to the contrary, however, Mosaic was never released as open source software during its brief reign as a major browser; there were always constraints on permissible uses without payment.
Marc Andreessen, the leader of the team that developed Mosaic, left NCSA and, with Jim Clark, one of the founders of Silicon Graphics, Inc. (SGI), and four other former students and staff of the University of Illinois, started Mosaic Communications Corporation. Mosaic Communications eventually became Netscape Communications Corporation, producing Netscape Navigator.
Spyglass licensed the technology and trademarks from NCSA for producing their own web browser but never used any of the NCSA Mosaic source code. Microsoft licensed Spyglass Mosaic in 1995 for US$2 million, modified it, and renamed it Internet Explorer. After a later auditing dispute, Microsoft paid Spyglass $8 million. The 1995 user guide The HTML Sourcebook: The Complete Guide to HTML, specifically states in a section called Coming Attractions, that Explorer "will be based on the Mosaic program" (p. 331). Versions of Internet Explorer before version 7 stated "Based on NCSA Mosaic" in the About box. Internet Explorer 7 was audited by Microsoft to ensure that it contained no Mosaic code, and thus no longer credits Spyglass or Mosaic.
In the October 1994 Issue of Wired, Gary Wolfe notes in the article, "The (Second Phase of the) Revolution Has Begun: Don't look now, but Prodigy, AOL, and CompuServe are all suddenly obsolete - and Mosaic is well on its way to becoming the world's standard interface":
When it comes to smashing a paradigm, pleasure is not the most important thing. It is the only thing. If this sounds wrong, consider Mosaic. Mosaic is the celebrated graphical "browser" that allows users to travel through the world of electronic information using a point-and-click interface. Mosaic's charming appearance encourages users to load their own documents onto the Net, including color photos, sound bites, video clips, and hypertext "links" to other documents. By following the links - click, and the linked document appears - you can travel through the online world along paths of whim and intuition. Mosaic is not the most direct way to find online information. Nor is it the most powerful. It is merely the most pleasurable way, and in the 18 months since it was released, Mosaic has incited a rush of excitement and commercial energy unprecedented in the history of the Net.
Scholars consider Mosaic to be the web browser which led to the Internet boom of the 1990s. Robert Reid underscores this importance stating, "while still an undergraduate, Marc wrote the Mosaic software ... that made the web popularly relevant and touched off the revolution" (p.xlii). Reid notes that Andreessen's team hoped:
to rectify many of the shortcomings of the very primitive prototypes then floating around the Internet. Most significantly, their work transformed the appeal of the Web from niche uses in the technical area to mass-market appeal. In particular, these University of Illinois students made two key changes to the Web browser, which hyper-boosted its appeal: they added graphics to what was otherwise boring text-based software, and, most importantly [sic], they ported the software from so-called Unix computers that are popular only in technical and academic circles, to the Microsoft Windows operating system, which is used on more than 80 percent of the computers in the world, especially personal and commercial computers. (p.xxv).
It should be noted that Mosaic was not the first PC browser; this was Tom Bruce's little-known Cello. The UNIX version of Mosaic was already making it famous before the PC and Mac versions came out. Other than displaying images embedded in the text rather than in a separate window, Mosaic did not in fact add many features to the browsers it was modelled on, like ViolaWWW. But Mosaic was the first browser written and supported by a team of full-time programmers, which was reliable and easy enough for novices to install, and the inline graphics proved immensely appealing. Mosaic made the Web accessible to the ordinary person for the first time.
Reid also refers to Matthew Gray's well-respected website, Internet Statistics: Growth and Usage of the Web and the Internet, which indicates a dramatic leap in web use around the time of Mosaic's introduction (p.xxv).
In addition, David Hudson concurs with Reid, noting that:
Marc Andreessen's realization of Mosaic, based on the work of Berners-Lee and the hypertext theorists before him, is generally recognized as the beginning of the web as it is now known. Mosaic, the first web browser to win over the Net masses, was released in 1993 and made freely accessible to the public. The adjective phenomenal, so often overused in this industry, is genuinely applicable to the...'explosion' in the growth of the web after Mosaic appeared on the scene. Starting with next to nothing, the rates of the web growth (quoted in the press) hovering around tens of thousands of percent over ridiculously short periods of time were no real surprise (p.42).
Ultimately, web browsers such as Mosaic became the killer applications of the 1990s because they were the first programs to provide a multimedia graphical user interface to the Internet's burgeoning wealth of distributed information services (formerly limited to applications such as FTP, Usenet and [(protocol)|Gopher]). This was also a time when access to the Internet was expanding rapidly outside its previous domain of academia and large industrial research institutions.
By 1998 its userbase had almost completely evaporated. After NCSA stopped work on Mosaic, development of the NCSA Mosaic for the X Window System source code was continued by several independent groups. These independent development efforts include mMosaic (multicast Mosaic) which ceased development in early 2004 and VMS Mosaic which is under active development as of November 2007.