Mosaic was described as "the killer application of the 1990s" because it was the first program to provide a slick multimedia graphical user interface to the Internet's burgeoning wealth of distributed information services (formerly mostly limited to FTP, Usenet and Gopher) at a time when access to the Internet was expanding rapidly outside its previous domain of academia and large industrial research institutions.
NCSA Mosaic was originally designed and programmed for the X Window System by Marc Andreessen and Eric Bina at NCSA. Version 1.0 was released on April 22, 1993, followed by two maintenance releases during summer 1993. Version 2.0 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 leader of the team that developed it, Marc Andreesen left NCSA-UIUC (University of Illinois) and with Jim Clark, one of the founders of Silicon Graphics, Inc (SGI) along with four other former students and staff of the university and started Mosaic Communications Corporation which became Netscape Communications Corporation, producing Netscape Navigator.
Development began in June 1993. The first releases were for internal testing only.
Mosaic's popularity began to dry up upon the release of Netscape Navigator, and by 1998 its userbase had almost completely evaporated .