Regarded as being the first widely adopted web browser, Mosaic was developed by a team led by Marc Andreessen at the National Center for Supercomputing Applications (NCSA) at the University of Illinois Urbana-Champaign in late 1992.
By January 1993, an early build for Unix was posted on NCSA's servers for free, attracting thousands of downloads a month. Within months (some sources say spring 1993, some say September), Andreesen and others ported the browser to PC and Mac, and by October a version was available for the Commodore Amiga -- all before Mosaic reached official 1.0 status in November.
Andreessen soon departed NCSA to form Mosaic Communications (now Netscape Communications) in April 1994 alongside Jim Clark of Silicon Graphics Inc. The company's first product, Mosaic Netscape 0.9, shipped in October 1994 and took three-quarters of the browser market within four months.