Mosaic was technically the first 'web browser', a program designed to interpret the HTML language, used for building web pages. Originally it was developed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, around 1993, and was ported to almost every major system around at the time, including PCs, Amigas, Ataris and the Archimedes.

The NCSA also worked with a company called Spyglass, Inc. (the business management side) and licensed its HTML comprehension code out to other companies to allow them to design web browsers, including Microsoft (for much of the original code of Internet Explorer 1.0 is based on Mosaic)

Mosaic was developed up to version 3.0, though from there (January 1997) development stagnated, though version 3 is a capable and relatively light-weight browser, although it cannot understand more complex tags. It can be found at archive.ncsa.uiuc.edu/SDG/Software/Mosaic/